The game designers on the official board were pretty mysterious on the topic. They did say that
- you shouldn't pray too often (the gods don't like whiners, apparently)
- you should pray only when things look dire (i.e. right before you shift-Q)
.
Apparently, prayers help those who help themselves.
I haven't played with it at all, but I'll remember that. Maybe solo priest would be viable using this ability.