Saying PoM is useless tells me a lack of skill/knowledge in class. Here are its uses for newer WHM's.

For Curing
Totally Precautionary. When you use it, you will never know if you have just saved the tanks life.

For Nuking Single Target
This is the best use for it. On a boss where you are with a tank you trust to keep hate. You will produce so much hate so be warned. DS Regen just to buy you as much time as possible. Now, to make the best use of the annoying animation lock PoM has, using the DPS rotation below I have found works best to keep you GCD uninterupted.
Starting the Nuke: Cleric Stance > Aero II > Aero > PoM > Stone II > Stone II > etc.
Finishing the Nuke: etc > Stone II > Stone II > Aero II > Aero > Cleric Stance Off > HEAAAAAL PANIC
Things that are important with this:
Aero is insta-cast so we have a moment of GCD where we can pop PoM and not interupt our GCD.
Aero does pretty much the same damage as Aero II.