Nowadays performing experience can make a nice supplement to experience received from killing, and give newbie priests a nice amount of xp to invest into fighting. The xp given appears to be 10 times the gp cost, and there does not seem to be any cap on the highest amount possible. To try and prevent experience farming by performing the same ritual in a short period of time. It will reduce the experience gained from each perform. Use as much rituals as possible to get an optimal xp return (and a better chance of tm'ing!) Praying also returns 10 times the gps used, but it doesn't seem to return less xp when used in sequence.
Some priests and other players team up in a group to benefit even more of this.
refer idlechasers if you're interested in joining them.