You changed your posts around, and I had a big reply. I have truncated it, the spoilers are unnecessary.
I basically see that every group is different and what works for one often won't work for the other. We obviously discuss things in terms of "most" games or "average" experiences, I simply suggest that those circumstances aren't nearly as prevalent as we think. A "general practice" may seem like a good measure for things, but I've learned without doubt that one size does not fit all in RPGs.
This just seems tautological, good = good. The question is whether it's a good practice in general. And, the answer, which I'll stand behind, is "absolutely not."
For the most part I agree, I was noting the exceptions because they end up being relevant. Every group has its own dynamic, and what we tend to talk about here is much closer to "etiquette" because you can't really be sure of anything where people are involved.
I don't recommend
hoping for certain exceptions, I just think it's important to be prepared for the likelihood that you are unprepared. If you enter a new group with a healthy philosophy about how to handle things and a good attitude, you will likely find things work out most of the time. The problem is that "most" can be as little as 50.000001% of the time. In the presence of more than one option the "most prevalent" can be infinitely smaller, just so long as the other options are smaller than the "most prevalent" still.
So you may see it as forcing a sort of method-acting on the players, but for all you know that will not only WORK but it will work well. It's not such a horrible thing to have a bunch of level 1 characters with some overlap, because they have lots of room to grow apart. It's also not so horrible to have a group that is extremely strong in one aspect of the game while weak in another, that just means you emphasize it when you work together. Method-acting works for some actors, not for others. Roleplaying that way works for some players, not for others. You don't have any idea what kind of batch you have until you've played with them.
Do I think it's a good idea all the time? No I don't, I just don't think it's as bad an idea as people are making it out to be, if only because players and groups can be so wildly different from each other. I've played with multiple groups of all-jokers, not one of them took the game seriously or even knew how to do so. I've also played with players who took the game way too seriously. How much fun I was able to have had a lot of variables, and while I do my best to have proper etiquette, sometimes it's not necessary. Sometimes it will get you left behind because the obvious thing to do is keep your mouth shut, other times it gets you way ahead because the group wasn't going to work well until you got there with your correct way of doing things.
"MOST" of the time things may work a certain way, but anyone who plays a dice-based game should be very familiar with how much one game can be different from another. Statistically a 51% chance of success isn't much better than the 49% chance to fail, it's BETTER for sure, but not so easily controlled as we'd hope.
Even when "most" means more than 51%, or 61%, you're still talking about people who are extremely variable.
As for "plants or moles" within the party
I also tend to agree normally it isn't a good idea. It worked in the game in which I experienced it though, and unlikely things like that color my perspective thereafter. My primary group at college was made up of weirdos and they enjoyed things that seemed impossibly boring or even offensive to me. I've played with groups of strangers at Origins and every experience was different. I have willingly attacked and killed other players' characters, had one of my coup de gras'ed on the order of my best friend's character, and had a session end after a yelling fight but the group came back together the next week. I've had the GM take visible pleasure in ending my long-lived character's life, complete with taking my character sheet and folding it up with relish.
The point is not that I've seen conflict, it's that I've seen people doing it differently every damn time. The "typical" adventure, the "general practice," the "average game," all of it barely exists in my experience. I just used the more striking experiences as an example, because they're all so varied. I'm far from the most experienced RPer, but I have been doing it for years and while I have yet to regret coming to the table with a sense of how I should behave in "most games," I've often found my restraint unnecessary or even damning on one or two occasions.
I get tired of playing entry-level characters as well, but eventually I've learned to sort of welcome their expendability. I can't get attached to them either, but that ends up working because they either die or live long enough for me to build a connection to them. This has caused me to invest less and less in the character at chargen, because I find myself much more invested after playing them. I don't even name them half the time anymore, which seems ridiculous - because it is - but I've often been so much more thrilled with a name that came from the game.
I was playing a shapeshifter in Shadowrun whose primary trick was to turn into a heavily-buffed giant tiger. I couldn't think of a name and was looking online with my phone at different languages to use for his name, I had finally decided on one and was writing it down when a fellow player started talking OOC. The party was about to enter negotiations with someone, he was saying that if the talks went south then "it's Tiger Time." I perked up right away, that was my name. It was goofy, but the character was goofy, and it just fit. The character's name became Tiger Time, and as with all of my Shadowrun characters I became very attached and fond of him.
My Warforged characters also rarely begin play with names. One ended up going by "Construct" because he was the only one in the party and that's what people called him anyway (I think he even started with a name), another went by "The Machine" because the names they received seemed so much more valuable than their serial number or whatever they might have gone by otherwise.
I have to play into a character's value, they don't usually start with much until they've earned it in-game. If people demand certain investments of me (Like a backstory, or the very reasonable demand that I name them) I don't mind, but I end up playing them all the way that feels right anyway, so having a backstory to live up to just seems like a hassle. In one particularly challenging years-long PbP game I find myself shedding almost every bit of the character's "identity" just to get my team through the missions alive. He was originally supposed to be selfish and generally a bit of loner (many of the characters were, it's an evil campaign) but very often I've had to ignore that RP to keep us from getting crushed as a party or to at least keep the GM from having to dispense too much mercy. The GM might have even hinted that he'd like more roleplaying from me, but he's good at making the fights tough, and my only salvation so far has been to keep him guessing.
For me I'm there to play, not write stories by myself or ponder personalities. I'm not the best at playing a character other than myself, but only because in my experience a lot of energy spent focused on your own character is a lot of energy you could have spent away from the table without taking other people's time.
This causes me to streamline my chargen and focus a lot on the party dynamic instead of my own character. Since this kinda works for me, I tend to find it frustrating when people haven't learned the same lessons I have. It's fine to have a different preference, I just place the table above the person at all times and prefer other people do the same.