In single player games it doesn't. Everyone is free to create their own experience. But if the game hits multiplayer, I don't want to see abominations around me. It spoils experience and immersion.
I'm preferring presets for this game, but that said, this is a game world where people sculpting themselves into abominations shouldn't be immersion breaking. This world has gene therapy, nanites, cyberware, bioware, even just vat grown replacement tissue, I'm sure even with just future cosmetics, people could customize their look to degrees we can't fathom today. With all of these things, some people are going to turn themselves into twisted protests against natural law. It is absolutely reasonable that your character would find those people disgusting or disturbing, but I can't imagine full on disbelief.
I think there are a lot of good arguments for
sliders *edit* presets, woops */edit*, like simplifying animation qa testing, personal preference, etc but I don't really see immersion being one.
My main hope for customization isn't in character creation, but if I get cyberware that isn't inside my body like an arm or something, that I can choose between obvious or not obvious, and if obvious having a few stylized choices like showing components (hydrolics, cabling, etc) or not, chrome, black, or other plating, etc.