8 hours in I bet my answers are here but I will reply anyway. Use bullet points to better separate my answers.
Unique experience in that guys are the norm for video games.
My first point leads to this. I can get a different experience than playing as a guy always. More so if I want to replay a game it makes that game fresh for games that offer no NG+. Mass Effect female VA was sort of better than male.
Dialogue is different. Kind of a repeat of what I have said about it being unique or different above. You gain a new perspective on how sentences can sound to the opposite sex (like hearing racial slurs in a game when you are that race in game but another in real life)
Sometimes there are benefits given to classes/races/sex/etc and that means I might want a certain character for that boost (pen and paper or RPG type games mostly do this).
Some games have different hitboxes for different characters, meaning sometimes women are harder to shoot giving a slight advantage (almost never find this).
As you can see I don't do it to RP as a female BUT I have in pen and paper games before and it was not something I would do again. I do it for some benefit to my gaming experience.