The Justice, if female and chio (heck, my photog did just that during my ROM, and even asked to take a pix posed with her. We all had a blast of a laugh about it so all was good fun!). If male and yandao, and if that turns you on, shoot!
The exchange of vows and rings, and of course,
Then the after-moments and social.
In betwen, try to capture all the subtle emotional moments like the nervousness, smiles, shyness, pride and happiness etc etc etc.
Some photogs regard ROMs as boring and dead-end, but a keen photog knows that there are lots of emotions and moments to capture.