I think description in a role play is particularly important. You don't know other peoples' characters, yeah? So I think it's important to give plenty of description to allow that character to interact with whatever they want. 

Example, character A is tall and thin and has long hair. 

Character B reacts to character A like a normal person would react to anyone. 

BUT THEN character A has red hair. 

Character B, holy shit, has the biggest fucking fetish for red heads. Suddenly, character B is going to have to react differently to this new information even though this already should've been known to the characters. Kinda breaks the realism of RP if a character has a delayed reaction to something he should already know about.

It's not usually details as basic as hair color that is skipped out on, however, but I think I make a point. Something pointless to your or your character might be important to another player and/or their character. Like, I have a female character I repeatedly use who looks like a boy. If I skip out on details that emphasize this, characters will interact with her as if she's just another woman. However, many, many characters react (positively and negatively) to a character that doesn't necessarily look like its assigned gender. So if I don't include these details that even I find trivial, I miss out on potential relationship (again, positive or negative) building.

Role playing isn't just putting up your work to be read like writing often is. It's writing for interaction. 

Details in writing, however...Well there's far too much variation in possibilities here in my opinion. It's hard to decide on good/bad rules of writing 'cause many an author can break these "rules" and still make a great story or poem or whatever.