I don't see the benefit for rated 10/15 bgs.

Sure, you're unkillable, but so what. You're going to just camp a node with 4-5 druids and keep people from capping it? For how long?

In 25mans, I think you could really help a lot of teammates with massive healing, but you occupy a lot of slots in a 10/15 BG for a team that won't do a lot of DPS.

I think you *might* be successful slowly wearing people down with Balance spells while you remain unkillable, but I think you'd suffer mana problems doing that AND you'd probably not provide enough burst to deal with any enemy healer (or DPS class with significant self-healing ability).

I think 4-5 Resto Shamans have more interesting potential, since you might still be able to pull off a bursty offense, but even then, I think it's better to have big firepower and some decent healing for survivability than be unkillable due to massive heals paired with gimpy offense.