In some circles including plus one's is social convention, but it doesn't mean you have to follow it. We couldn't, because our guest list was already over-the-top large and space was be tight. If you know friends or family members that aren't in a relationship but don't know a lot of other people that will be attending, it is a nice touch to allow them someone they know to bring along-but you don't need to feel the need to extend this to every single person you're inviting if you feel they'll survive just fine at your wedding.

Remember, the rule is that if the invitation includes "and Guest," your friend can bring someone. If it only has your friend's name, you have every right to inform them they can only bring themselves if they try to bring someone else along. DON'T let invited guests bully you into allowing them to bring people that aren't invited. If they add extra people (like children, even though you didn't intend any children to attend), the best thing you can do is contact them immediately and tell them, politely, that your seating is limited and you are simply unable to accommodate them. It's not fair to other guests (and other people that wanted to be invited but weren't) if there are people who basically crash your reception. You won't have time for crowd control at your wedding, so handle it right away, as uncomfortable as it may be.