Quite honestly? Standing and Walking. Seriously.
A wedding rehearsal is nothing more than deciding where everyone is going to stand, from what direction they are entering, and who is walking in front of and behind whom. You really are not having a wedding rehearsal, you are having an enter and exit rehearsal.
A good wedding officiant will be able to guide a bride and groom through the ceremony itself just with the typical stage directions written into the ceremony, body positioning and hand motions. None of this is distracting to your guests who will barely register, if at all, that this is precisely what the officiant is doing. 99% of a wedding rehearsal is consumed with details like deciding whether the bride or groom will stand to the officiant's left, where the parents will sit, whether the groomsmen will walk in with the bridesmaids or already be standing up front, and whether the flower girl will walk with the ring bearer or stick her tongue out at his retreating back. Keep in mind as we go forward that "attendants" are simply your bridesmaids and groomsmen. It doesn't refer to your attendance. That's your guest list.
Rehearsals are sometimes absolutely necessary, but often a matter of personal preference. I leave it to the bride and groom's discretion but do have a "rule of thumb" and an "exception to the rule of thumb." While the bride and groom have two of the easiest parts to play--logistically anyway-- if you have several attendants on either side, consider their nerves on the big day. I once officiated a formal wedding that had five attendants on each side and no rehearsal. The bride and groom were incredibly laid back and prepared for whatever their wedding turned out to be. Their attendants were a mess! It took three of us to calm these ten people down, line them up and assure them wherever they ended up positioned for the wedding would be fine with the bride and groom.
If you only have honor attendants (maid/matron of honor and best man) you do not need a rehearsal. If you have a maid of honor, a matron of honor, two best men, six bridesmaids, six groomsmen, two junior bridesmaids, a ring bearer and a flower girl you definitely need a rehearsal. The weddings in between constitute a judgment call on your part. First of all, rehearsals can be great fun. The rehearsal is a tradition that allows members of the wedding party who may not know one another to become acquainted. It provides an opportunity for the two families to socialize as well as mentally and emotionally prepare themselves for the big event.
Rule of Thumb:
Exception to the Rule of Thumb:
- 0-4 attendants: No rehearsal necessary
- 5-6 attendants: Worth considering a rehearsal
- 7+ attendants: Schedule a rehearsal
If you are getting married in a private home seriously think about having a rehearsal regardless of how many attendants are in your wedding party. Home weddings are lovely, but they are not natural event venues. A rehearsal will alert you to issues you may not have considered previously. You do not necessarily need your officiant for a home wedding rehearsal, but you should discipline yourselves to conduct at least one and impress upon the other participants the importance of what you are doing. It really will help alleviate some of the stress on your wedding day.