All my couples ask me this question. Should we have a rehearsal?
And my answer is always the same - it depends on the couple!
For some couples, the peace of mind after having a walk through beforehand is exactly what they need. Working out where everyone is going to stand, or timing the entrance of the bride to the music, or just having an opportunity for your bridal party to meet and hang out is really nice.
Other couples prefer to have it all unfold naturally on the day. Plus, there's always a bit of time before the ceremony starts to figure out where people might stand. A good celebrant will always discreetly guide people through the ceremony, if people are looking lost or unsure of where to stand or what to do.
So have a chat together and decide what is going to be right for you both. :-)