Building temples (noob question)

[Meglobob]

I have noticed in most my MP games that lots of players build temples, loads of them, in provinces without a castle.

Is this really a good idea?

I personally only build a temple/laboratory where I have a castle or in a province which gives me a special unit type (and then I protect it with at least PD 30, if its not worth building a castle), in order to keep my dominion up I just recruit priests. A temple costs 400 gold a go, while a priest costs 50 gold or less for some nations. 2-3 priests can do the job of 1 temple, I find and have the advantage of being movable. I am thus saving 250 gold and getting more benefit, so I think my strategy is better.

What do other players think? Is my strategy flawed? Am I missing something?