Well depending on the characters traits makeup can help for multiple uses. As you know, anime characters don't exactly have "perfect skin" lol (unless the creator made the person not have perfect skin). So usually people use foundation and concealer and all that jazz to make that "perfect skin" look.
Contouring is also a big thing, for example, if a female cosplayer wanted to cosplay a male cosplayer, they would have to make the contouring to a male face structure.
So overall, makeup can be an essential part of cosplay and can make people look completely different, depending on how you use the makeup but at the same time, makeup isn't THAT important. I hoped this helped a little?
I'm a total amateur myself, I just started learning bit by bit.
Youtube tutorials help a lot!