It's rare to discuss your wedding photos and not have someone say something akin to ‘have you thought about asking Uncle Tommy to do the photographs, he took the ones at our Rita’s wedding and they turned out quite nice!’.
But unless your Uncle Tommy or whoever has the letters ABIPP, AMPA or equivalent after their name, then chances are that any professional photographer you hire will produce significantly better shots than any of your guests.
Whilst we would strongly recommend that you use a professional photographer, a ‘budding amateur’ can come in handy for capturing images that would otherwise have been missed. Whilst they may want to follow you and the photographer around the grounds of the Reception venue, this is not a good idea. Instead why not ask them before hand if they would like to photograph guests and the rest of the Wedding Party whist the ‘official’ snaps are being taken.
You will find that many professional photographers will be willing to incorporate decent amateur shots into an album to enhance the feeling of completeness, but if not, a smaller reportage style photobook to sit alongside and complement the main album is always a welcome addition. A brief chat with any ‘budding amateur’ before hand should allow you to firmly, but politely, refuse their kind 'official photographer’ offer but instead offer them a role in the day that both you and they are happy with.
Of course, if the wedding budget has already been blown or if the friend/relative in question is a pro, then there is no reason why not to use them.