Prayer and piercings have never been something one would think would be combined. Unless one is praying for a piercing to turn out good and not reject or get infected. But oh just you wait there is the prayer piercing.
The payer piercing is a piercing on the outer edge of the hand and usually done as a surface piercing. Seen best when someone would be praying, hence the name prayer piercing. It looks best when done on both hands. But symmetry may not be for everyone. I am guessing that it could be done horizontal or vertical.
The arguments against this piercing would be that it is a surface piercing which have been known to have a very high rejection rate. That makes me think that someone could easily just get this done as microdermals. There would be a much, much lower risk of rejection. Of course there is still is the risk of the piercing snagging on things, or getting rubbed on things, due to the area of the hand it is on. When you think about it, that area rubs against a lot of stuff.