For example, what's the difference between 那边儿 and 那边? When writing in Chinese do I need the 儿 because I've heard people say both.
Well 儿 can appear in formal language. We Chinese speakers don't really care so much. Actually it can mean something different with or without 儿 in different contexts.
when you writing an essays or something like that, or in a informal communication(daily chat) you can use “儿” as you like ,but in some formal case, especially writing documents,you'd better not use it,