This is up to you, for me when I got married I wanted to see people's faces during the ceremony, especially when my wife walked down the aisle, I would therefore advise that you ask people not to take photos during the early parts of the ceremony.
During any formal group photos it's essential to have people looking at the official camera rather than at everyone who has their phone out, so for the formal shots we would ask that no one else takes pictures.
Otherwise the more photos people take, the better!