My son has been dairy allergic since birth. We once took him to Pizza Express and it made us realise how bad his allergy was when he had a reaction from the fumes in the restaurant. That might seem a really obvious outcome if you have family who have allergies and at the time, when we were so new to it all we hadn't realised.
Pizza is clearly something we stayed away from until we were away on holiday with my husbands family in Wales (I dislike Wales a lot, another story) and one of the family suggested we try pizza without cheese. My son absolutely loved it and we've made it a few times since to equal fanfare. You can, of course, if your diet allows add cheese. My favourite is making it into a calzone (folded pizza).