As great and as versatile as your HoTs are, they can't handle every situation you come across while raid healing. There will be times when a target needs a big heal, and they need it now. When you don't have time to wait for ticks, you have to bring out your direct heals. Direct heals, for those who don't know, are healing spells that do all of their healing in one shot... no ticking, no stacking, no waiting.
Let's take a look at our arsenal.
3 second cast (out of the box). With talents and gear, this spell can heal for roughly 12k, crit for 16k, and be cast instantly with the Nature's Swiftness ability. Some druids will tell you this spell should hardly ever used. They're wrong. The NS/HT combo saves a life atleast once per boss fight.
Over zealous hunter pulling aggro early? No problem. Finish stacking your HoTs on the MT, then bring the 'tard back from the brink with a 16k crit.
Main tank down with the boss at 10%? No worries, mate. Use this to keep your top DPS alive while the OT gets in there to taunt.
Everything going right in your raid? Grats! You can still use this spell to your advantage. Let your tank tick down to 50% hp while you HoT up those taking AoE damage, then pop HT to bring the tank back full.
1.5 second cast (out of the box). This is the druid version of flash of light. Without the nourish glyph, this spell heals for roughly 3.5k and crits for about 6k. With the glyph it heals for 6k, crits around 10k. This is your spam heal when you're single target healing, and trust me when I tell you, druids CAN single target heal extremely well. There are many talents in your build that will buff the crit rate of this puppy, and with 3/3 in living seed, one cast of this spell will pump out 13k healing. Not bad for a 1.5 second cast.
Instant cast (15 second cooldown). Can only be used on targets with Rejuvenation or Regrowth ticking on them. This spell is probably my favorite cast in the spellbook. Available every 15 seconds, it takes all the healing power of a rejuv or regrowth and delivers it to a target in one shot. And if you get the swiftmend glyph (which you're crazy if you don't) your HoTs will keep on ticking essentially doubling the healing power of rejuv and nearly doubling regrowth. Swiftmend heals for 8k (for me) and crits for 12k.
Breakdown: Compared to other classes, druid direct heals seem slightly underpowered... which is why most people think we're not great single target healers. But when used intelligently in conjunction with our HoTs, there really is no fight a druid can't main tank heal.