kosmion wrote:ive heard disc is good for tankhealing
When people say this, I have no idea what they are talking about. Standard healing build is 21/30/0, I don't see any talent you can get by going deeper into the disc tree that would have any impact on tank healing at all. If anything, you are losing talents from the holy tree that make ALL healing better.
By going deeper than 21 in disc you can get Martyrdom, Imp inner fire, Imp mana burn, Mental Strength, Force of Will, Power Infusion... I don't see how any of these would make you a better healer in any way, never mind for healing tanks specifically. 10% mana is at best equivalent to +10% base healing and power infusion only lasts for 15s and has a 3min cooldown.
If you go deeper than 21 in disc you lose Spiritual Healing (+10% base healing on all spells) and Spiritual Guidance (increased damage and healing by 25% of spirit).
You won't be completely useless in PvE but it certainly is not an optimal build for raid healing. Whether that matters or not comes down to the guild that you are in. If compared to the rest of the priests in your guild, you use more consumables, have better addons and pay attention more, you will probably still do better than them. If your guild doesn't care about absolute min/max'd raiding builds, then they might love you for the power infusion on their mages/locks and not care if your healing performance is a bit lower or you don't have imp fortitude.
When it comes to PvP the traditional tank/heal/DPS get's a little weird. Nobody is going to let you stand around bombing heals, they go straight for you. This means that when it comes to PvP, you need to be able to heal but because of that, you are primarily a tank. Talents like Improved inner fire, Martyrdom, Spell Warding, Blessed Recovery become really important. Unfortunately, these talents are also completely useless in PvE where if you get hit, you are probably already dead.