I dont understand the bit about the art style evolution being impacted by having a model sheet really 
I have made very simple model sheets so I can easily grab the colors needed also 'caus my characters have a few details that I keep mixing up which side they have it on so I can quickly look at a model sheet instead of going back looking at older pages.
My art style is not affected by this model sheet the least, and usually when I feel my art style have changed I just make a new model sheet to fit my current style or if the characters maybe change outfit after a couple of episodes.
And the model sheet helps me a bit caus I got characters with big hair that is a bit curly and Im bad at drawing that esp how it looks like from behind so I can easily check my model sheet what my plan was for the hair looking from behind and stuff like that...
Model sheets is not something you HAVE to do but it CAN help you out just quickly checking for details and stuff to draw faster so you dont make all these finished pages and then realise ops they have that detail sometimes on the right side and then one page it pops on the wrong side and then back again (ive done this a couple of times, its a pain going back to fix it lol )
Also, you get some nice art and reference for ppl who might want to draw your characters 
I dont use model sheets from time to time but then I feel like I keep messing things up to often I just make one and print it to have easy access when I sit and draw. Its really up to anyone what they feel like, never feel like you HAVE to do certain things caus other artists claim yuo have to, it can stop your own progress as well, it did for me in the beginning, then I just felt like making a model sheet for fun and it helped me out and yay.