I've been to many Manitoba socials. Open to the whole town and they are a hoot. Certainly not an engagement party by any means. Just a place to party with cheap drinks and random people!
(Tickets to get in were usually like 3-5 bucks) The host take on the risk of hosting a party for a bunch of randoms (Well maybe not that random, it is a small town after all) and in return they get some cash towards their wedding.

I wish I could convince BC people they were a great idea. haha. Just a riot.