Thanks everyone, some good food for thought.
The main reason I care about this, as a largely homebrewed DM, is that I do in fact have characters in the campaign that are more powerful than the PCs. I don't think it is fair to not clearly hint to the PCs that the opponent is out of their league. And on top of that my PCs are largely obsessed with completing every single encounter so as not to miss absolutely anything, which means searching every last detail and fighting everything do or die. So as soon as they see anything they latch on like rabid weasels.