While I would say I always like to make a character around a theme or concept more than around mechanics, I had just entered a discussion with somebody that prefers the character 'crunch' to help them make a character and understand the 'things you can do'.
In a sense, everything is some measure of "crunch", and needs to inform the character creation. A "theme or concept" has to fit with the proffered race and class combinations, for example. A player needs to understand the scope of their options to create anything. And I suppose some players may never have heard of "elves" before, so the existence of that race option in the game opens up a whole new set of concepts for them.
Likewise, a player might not have much idea about, i.e., fighting styles for a warrior. Extra crunch like unique bonuses and penalties for each weapon type, fighter style kits, or specialization rules might provide that player with all sorts of character concepts, which itself would be useful.
The thing is, in a low crunch game all of those same character concepts are typically already available, and adding the crunch to codify them really only eliminates any
other options -- those for which there is no crunch. Sure, more crunch for each option can be added, but here I'm looking at the crunch that already exists, as it pertains to the player's perceptions at character creation time.
Examples and prose and such of the same character concepts might be just as informative, but maybe not as readily absorbed by the sort of player with a more mathematical approach to conceptualizing. Perhaps ideal in this regard would be for the player to
read the options for a high crunch game, and then create a character for a low crunch game. But I suspect that such players will also prefer the greater measure of regimentation provided by a high crunch game during actual play.
I think it's mostly an issue of left- vs. right-brained dominance. Tabletop RPGs are a neat mixture of both, with low-crunch favoring the right brain and higher crunch favoring the left brain. I think a lot of RPG players are relatively centered on that spectrum and enjoy the sensation of exercising both sides of their brain together. But few will fall
exactly in the middle, and where the balance sits for each player may partially determine how much crunch they'll enjoy the most.