When all priests were given Hymn of Hope, all the Draenei of the world died a little on the inside. The 8 second cast for 8% of base mana is, yes, lackluster. However there are uses in fights when this can be used, safely.
Yes, there are the situations when your party members need mana (or you do) and using it is tempting. If that is the case, communicate with the other healers… however think before you assume doing it is ok. If you are low on mana, it usually means the other healers are too… are they able to pick up your slack for the next 8 seconds? Or consider using your Guardian Spirit as well.
Lets discuss fights/phases that you can typically safely use Divine Hymn:
1. Malygos Phase 2 Transition – You have 15 seconds or so during the transition where Malygos has a dialog and the adds start to arrive. In my guild I instruct all non-shadow priests to use their Hymn during this transition. (If you have more than 1 in the same group its quite nice and a good deal of mana restoration)
2. Loetheb - taking time to stop assisting the DPS with Shields, Holy Fire, SWP, etc to channel this spell before the healing debuff wears off is another good place to use this spell. Returning mana to the “real dps” classes is better than you getting off a couple of 2k-3k smites.
3. Gothik the Harvester – in between waves you should have enough time to get off a full channel before you get more mobs coming at ya.
4. Anub’Rekhan Kite Phase – While the tank is busy running around the arc of the room the MT healers should be able to pop Hymn and be able to return mana to the party while the non-priest healers keep up the Add-Tanks who are on the Crypt Lords & Corpse Scarabs who may still be up.
Completely useless? Hardly.
Just find a time you can use it, and use it! However, that doesn’t mean I’m not hoping Blizzard changes this so its not a 8 second channel… oh no, quite the contrary.