Weddings have a thousand moving parts, as such rehearsals are a needed aspect for all weddings. However, is your ceremony musician needed at that rehearsal? Many bride's have asked me this question over the years. The short answer is maybe, but probably not.
If you hire a musician that is experienced in weddings, you most likely will not have to pay for them to attend the rehearsal as well. There are some exceptions. If, for example, your wedding ceremony has an awful lot of moving parts and is quite different from a traditional ceremony it would be beneficial to hire the musician to attend the rehearsal.
As a professional harpist I've performed at more weddings than I can remember to count, and only one wedding rehearsal. The reason behind not needing to attend the rehearsals is namely preperation and experience. After playing for weddings for more than ten years you learn a couple tricks to make everything run as smoothly as possible.
One of those tricks is the consultation. For all my bride's I provide a consultation to not only choose the wedding pieces, but to get as detailed a plan for the ceremony order as possible. From this consultation I want to know exactly how the bridal party is composed, where they will be entering from, and the order in which they are walking down. The day of the wedding I also check in with the officient to go over their closing words for the ceremony. Along with this, all of my pieces are arranged so that they can be played as long or as short as needed for any processional.
Another reason that rehearsals are not generally necessary is the element of change. There is often a sense of the unexpected with weddings. Things do happen! Bride's rush out before their music starts, and little ringbearers never make it fully down the aisle. As such, the musican has to be on their toes and watchful during the ceremony.
This doesn't worry the professional musician. In fact, a sense of the unexpected is expected at weddings and through their career musicians attain a 'feeling' for how cues and entrances should develop. For those bride's who have worries, I hope I've cleared up the question of if rehearsal time is needed. In the hands of a professional musician, your ceremony will be flawless and smooth and your guests focus will land where it should, on you!
*Please note that this post is in my opinion and is merely meant to guide you. Each professional musician will have a different set of expectations and guidelines regarding rehearsals. If you are hiring an amateur musician or a family member/friend, rehearsal time would be necessary.