Less burst (damage) is good burst (damage)
But there's no need to panic just yet, because Blizzard isn't trying to make healing harder and this doesn't just mean that everyone in groups is going to be dying a lot more -- it means the whole nature of the game is changing. Right now, healers can heal for so much that to challenge them Blizzard has to create fights that cause huge spikes of damage. In Warlords, healers will be healing for less but we'll see fewer huge bursts that need them to keep everyone at max health all the time, which Blizzard hopes will make healer gameplay more interesting than playing health bar whack-a-mole. (If this sounds familiar, it's also something Blizzard tried to do with healing changes back in Cataclysm. As you can see, it didn't really stick -- but hopefully Blizzard has learned from their mistakes.)
If Blizzard does manage less spike damage, that could be good news for all players, because it gives anyone in a group the opportunity to hit those damage reduction or healing abilities instead of winding up instantly dead. At least in theory, less burst damage mean that every player can break out of their fixed rotation and respond to damage when it happens, beyond just moving out of the fire.
Speaking of moving out of the fire...
Blizzard is killing a lot of instant-cast healing -- or at least, giving it a cast time. Instant casts were important because healers could cast them on the go, to top off group-members while everyone was repositioning themselves to get out of fire, green goop, or whatever ick the boss was hurling their direction. Not being able to heal on the go as easily could mean a couple of things for future group play: either they're going to require less movement or they're not going to need you to move and heal at the same time.
Either of these options is better for groups. Less movement means everyone gets to focus on playing their character as best they can instead of zigging and zagging around. But no need to heal on the go would at least imply that moving won't happen during periods where there's a risk of high damage -- especially not to the entire group. This means less chance of dying across the board -- and less stress on healers to constantly cast AoE heals to keep everyone topped off.But what does it all mean?
We're still just seeing a piece of the puzzle -- not the entire thing. But these particular puzzle pieces paint an interesting picture for future group content that features less instant death damage spikes and more intelligent decision-making across the board. But as this could still change, we'll keep our eyes open for more info from Blizzard.