Why WOULDN'T a spellcaster take ranks in Concentration?

[Bozwevial]

That wasn't the point I was making at all. The point I was making is that turning it into a you fail check just means everyone's going to gravitate towards something else, and that something is stronger anyways.

So if I want to spend my skill points on diplomacy and knowledge arcana, I should just stay away from close combat and I'll be fine without concentration?

Awesome.

Environmental hazards and such cap out at a DC of 20, I think. And that's for something major like an earthquake.

The only other things you'd probably have to worry about are spells and effects that specifically force a check and someone readying an action to hit you during casting, but if you can attack a spellcaster and actually make it, why not just attack him then and try to take him out instead of waiting for him to start casting?

[Basket Burner]

That wasn't the point I was making at all. The point I was making is that turning it into a you fail check just means everyone's going to gravitate towards something else, and that something is stronger anyways.

So if I want to spend my skill points on diplomacy and knowledge arcana, I should just stay away from close combat and I'll be fine without concentration?

Awesome.

I thought that we were talking about gishes here.

[X-Codes]

I guess if we make it BAB + Casting Stat or BAB + Con Mod, it would be better than just straight BAB.  In any case, something like...

Wizard 5/Mindbender 1/Wizard PrC 10 has...
+8 BAB
+8 Int
=+16 Concentration check

Highest level spell he can cast is 8th-level, which has a Cast Defensively DC of 23.  He fails 30% of the time.

Wizard 6/Swiftblade 10 has...
+13 BAB
+8 Int
=+21 Concentration check

He can cast 6th-level spells, which have a Cast Defensively DC of 21.  Never fails.

Crusader 4/Wizard 2/Abjurant Champion 5/Swiftblade 5
+15 BAB
+4 Combat Casting
=+19 Concentration Check

He can cast 5th-level spells, which have a Cast Defensively DC of 20.  Never fails.

Now, these checks *might* fail if you smack them hard while casting, but that could be true of the actual Concentration skill, too.  In any case, the check mods aren't so far off the RNG that you can ignore them and still be awesome.

[Mixster]

Environmental hazards and such cap out at a DC of 20, I think. And that's for something major like an earthquake.

The only other things you'd probably have to worry about are spells and effects that specifically force a check and someone readying an action to hit you during casting, but if you can attack a spellcaster and actually make it, why not just attack him then and try to take him out instead of waiting for him to start casting?

Awesome.
So the answer to the OP is:
GOD wizards don't need to max out concentration.

I guess if we make it BAB + Casting Stat or BAB + Con Mod, it would be better than just straight BAB.  In any case, something like...

Wizard 5/Mindbender 1/Wizard PrC 10 has...
+8 BAB
+8 Int
=+16 Concentration check

Highest level spell he can cast is 8th-level, which has a Cast Defensively DC of 23.  He fails 30% of the time.

Wizard 6/Swiftblade 10 has...
+13 BAB
+8 Int
=+21 Concentration check

He can cast 6th-level spells, which have a Cast Defensively DC of 21.  Never fails.

Crusader 4/Wizard 2/Abjurant Champion 5/Swiftblade 5
+15 BAB
+4 Combat Casting
=+19 Concentration Check

He can cast 5th-level spells, which have a Cast Defensively DC of 20.  Never fails.

Now, these checks *might* fail if you smack them hard while casting, but that could be true of the actual Concentration skill, too.  In any case, the check mods aren't so far off the RNG that you can ignore them and still be awesome.

Hmm, that actually works, and makes combat casting somewhat viable.

Even something way more on the wizard side of gishy works relatively well:
Wizard 4/Warblade 1/SpellSword 1/Thrall to Demogorgon (or that dragon slayer guy) 1/Abjurant Champion 5/Eldritch Knight 3
+4 Int
+13BAB
+4 Combat Casting
=+21 Concentration
Can cast 7th level spells = DC 22 to cast defensively.
Doesn't fail.

So basically this works for making gishes still able to do their thing, while removing the ability from a wizard to run around in close combat and cast spells.

Since no-one likes casters, I don't see why this is a bad change.

[PlzBreakMyCampaign]

Level checks? I agree. Those poor clerics with their skill point taxes. T1 isn't enough.

[cvar]

Well if your GM doesn't play monsters smart you could skip out on it.  I don't think our druid ever took an AOO from casting last game and readied actions were almost non-existent NPC side.  I think they did it once and were foiled by us casting an illusion into the room first.

But if your GM plays monsters intelligently (kill the squishy apeman who keeps wiggling his fingers!!) it'd be a good idea to keep it topped out or at least find ways around being attacked.

[StreamOfTheSky]

Level checks? I agree. Those poor clerics with their skill point taxes. T1 isn't enough.

Surely, this was a major rallying cry in the creation of Pathfinder! 

[Libertad]

Level checks? I agree. Those poor clerics with their skill point taxes. T1 isn't enough.

Surely, this was a major rallying cry in the creation of Pathfinder! 

To be fair, they did buff up the Paladin.  But the Fighter got some abilities that were only useful in limited circumstances (reduced ACP, bonuses to saves against fear, etc.).

They did nerf the Druid's Wildshape significantly.

But this is for another topic.

[Jackinthegreen]

In my last game I played a cleric, and not having many ranks in Concentration actually proved helpful for us.  The DM essentially created dark versions of all the PCs, and we duked it out.  Our cleric/wizard/MT cast a fire wall on the enemy, forcing them to make Conc checks to cast spells.  Since the dark versions used our own stats, my evil equivalent failed his check and wasn't able to cast at all.

This kind of encounter is quite unikely, but it is an example where not taking ranks in Con proved to be beneficial.

[SorO_Lost]

sorcerers shouldn't be casting from combat anyway (5 foot step out of reach, people)

Only works with medium sized humanoids.
Pretty sure that list is tiny.

Did you mean Move Action + Tumble instead?