I just encountered a strange situation. Being that the wedding is a vacation for our guests, we addressed our invitations with a guest for our friends that are in and out of relationships being that I wouldn't really know what their status will be when the wedding comes around. If my friends/family members have been in relationships I addressed the invite with their SO's name. Now we have guests bringing random friends we've never met or even heard of.
Our one friend who is single did ask before he invited his buddy after trying to figure out who was already invited that he could room with. I was obviously okay with him bringing his friend since he plans to stay for 6 nights and none of our other friends that are going are able to stay that long. I wouldn't want him to shorten his trip because I said no. I still kind of wondered in my head if he was joining at the ceremony/reception, but figured he would be as opposed to sitting around the resort by himself for several hours.
My fiance has two female friends that were invited and are also on and off in relationships. They decided to come and room together, which is great, but they also told us they are bringing a random friend we don't know. I think the issue I have with them is that they didn't ask us about it first (they booked and then told us). I know it comes with the territory of having a "guest", but if I received the invite I would have assumed it was for a boyfriend/girlfriend and not just any friend I'd want to bring.
I'm just sucking it up and trying to convince myself that not everyone will do this (I just don't want 30 guests I don't even know at my wedding since I wanted it to be intimate).