Great feedback really appreciate it but if u said that one been invited n just njoy the banquet I wondering when will he/she be able to practise or train if one wanted to be a wedding photographer... But I agree the part where that he/she have to be carefully when taking shoot to prevent from distracting the main photographer...
If you want to practice and learn, you might be better off joing a photography course. And if you are really very interested, don't take a camera to the wedding and start shooting off. Obvious what the primary photographer/s is/ are doing and ask them question if you are not sure and they are free.
Then look at your friends wedding photos, and think of what you like about these photos, what the primary photographer did that hit that spot.
If you are too busy shooting your camera... you won't have the time to look and learn from the professionals.