I get asked this quite a lot, I normally say 'I don't know I'm not you, I however don't have a cum limit but if we are 28 mins into a 30 min booking and you are trying to get a 3rd shot out then you are taking the piss!
I normally get a very positive reply back saying that's not the intention they just want to know they can go again if they cum early.
I used to think it was timewasters or fantasists who just wanted to wank etc but personally I think it has a lot to do with having bookings where they have cum early and then been refused a second round
I'd rather have 2 or 3 short rounds full of fun and passion where a guy can't hold out than 1 round that lasts 50 m8ns and no matter what I do he doest cum till he let's himself, that's a total passion killer