I'm only speculating in regards to closed roleplays, as I've never hosted one nor been invited. (aw)

I would say closed roleplays may be fun if everyone knows one another (say a group of friends or long time roleplay pals). However if you don't know one or two of the players and you're invited based on someone recruiting you based on your posts around the site, as well as your tastes, it could be daunting. Someone is picking you and it could put some pressure on you if you feel new or out of your depth. On the other side, if you're a GM and pull certain people together, the pressure is on. Did you pick the right people? Will they stick around and not wander off? I feel like closed roleplays can be littered with mental pitfalls but then again, I'm only speculating here.

My heart lies with open roleplays because it lets me meet new writers and doesn't limit me if someone new joins the site who would be great for the story and I have yet to meet them.

It's that simple for me.

Besides in an open roleplay, you can still invite people to join who might have fun, but with it being open,it still allows for fresh writers to join. Eheh.