I have taken both a Rolleiflex and Pentax 67 a few times. The reason is I like the Rollei better and I like the square format but the Pentax has changeable lenses, wide angle for a group or tele for some portraits. The truth is that neither is a great camera for most of the wedding photos. You are much better off with an auto focus auto exposure 35mm for the ceremony and all the candids.
When it comes to delivering your work to the couple and you have shot film, you usually will give them some small machine prints. The ironic thing is that from a 35mm neg you can get a 4x6 machine print where from a 67 MF neg you will get a 4x5 print and from the Rollei you will get a 4x4 print. So the couple looking at the work will see the bigger camera as making smaller pictures than the 35mm camera. And at that size the larger neg doesn't do you any good over a good quality 35mm camera lens.
My working method when doing film weddings is to shoot set up portraits with the MF and then get them printed on 5 inch paper so the prints are larger than the machine prints from the 35mm. Then I will shoot the ceremony and the reception with the 35mm.