Basically it's for diversity of body types, if you're designing a character for something whether it's stylized or not there should be a familiarity with all kinds of anatomies. For example, I'm currently working on a range of different character concepts for a game where one of them is enormous and fat. The character is also a tank/ damage soak, so by being larger and clearly just a pile of meat his silhouette instantly conveys to the player what his role is in relation to the others. The difference is if you're drawing something it's essentially just a series of shapes and lines, and you can make them look appealing no matter what, in real life fat is 100% of the time fucking disgusting to look at. There's a reason no artist ever draws in cellulite, stretch marks, compounding rolls and folds etc. on fat characters.