It's probably happened once or twice and went something along the lines of this...

[quote]- Sees interest check
- Drops a "Interested" Post
- Sees a friend also drop a post
- "OMFG! You gonna join this too? This is AWESOME!!!!!"
- OOC has started
- "Let's create some wicked ass characters!!!"
- RP starts
- Places up a post
- "This is gonna be great!!!!!!!!!!!!!"
...
...
...
- GM Drops soon after starting the RP
- [url=http://www.nooooooooooooooo.com/]"Noooooooooooooooooooo"[/url][/quote]

So in summary, it's an advantage because you know the people you are RPing with and I know I can get along with them fine. I just wouldn't join an RP simply for that basis alone. If I'm not interested fully in the storyline and theme, I'm not going to present a half arsed effort just to play along with friends.