When you and your partner are preparing a guest list and you're inevitably considering whether to invite someone, consider this: if having them at your wedding doesn't excite you, it's usually a good idea just to not. There can be an enormous amount of pressure to invite everyone you know (and your parents know)--distant relatives, co-workers, classmates, old and estranged friends--but really, you shouldn't, unless you're throwing the event of the season in the Hamptons.
During post-wedding image viewing sessions, sometimes we hear things like, "I really didn't get to see many of my guests", or "who was that person in that photo?" or "we never got to talk to them!". Narrowing your guest list to those you really want and need at your wedding makes it easy to get quality time with them. Oh, and that stress level? Down it goes! You and your partner will have a difficult enough time trying to see those you love on your wedding day between makeup and photos and dancing and eating and the tossing of bouquets and and and... Why spend the energy (and, yes, money) on those you don't really want there, when you could surround yourself with loving and meaningful individuals that are likely to be your friends for a really long time?
So when you're going through that list of friends/relatives/co-workers/classmates, and a name makes you fret, take them off the list when you can. Invite happiness, care, community and love to your wedding. Leave the rest behind.
P.S. A Very Important Etiquette Disclaimer: if someone other than you is paying for a bulk of the wedding, their advice on the guest list usually must be considered, and therefore you may end up with guests you don't know well or that must be invited for social reasons. In that case, embrace it--it's part of the process.