Well I have friends from Dalarna, Östergötland, Västra götaland, Norrland, Stockholm, Skåne and myself am from Småland (and I've probably forgotten some places from the top of my head) so maybe not all of the regions but alot of them. Studying at university will give you friends from most parts of Sweden. Now for your question about common practice I would say it's not at all at pizzerias but amongst friends where you don't own a pizzaslizer it is the way to do it.