My pet healing reasoning:
Second mob, if trash mob I let come to me due to healing and trip freeze trap, continue firing through until first dead, pet comes back automatically and tell to attack frozen mob, reaggros on pet in a heart beat. Easy grinding.
If 3 mobs, I'll have pet attack 2 of the 3, get at least a growl off on two of them, multishot to pull the unhit one back to me and repeat as above, chain trapping frozen mob, all the while staying on the mob my pet has. Interestingly enough, the HoT lets the pet finish off the two normal mobs at or really near full health to engage the third. If I'm low on mana I can back off to autoshots and just keep mend pet up. Again, easy grinding.
I really don't like my pet taking a beating. Against multiple mobs it's so easy to have a string of bad luck or a moment of inattention put your pet on the ropes. If I lose the pet, I have problems winning the fight. If pet near max all the time, even unforeseen adds can be targeted, attacked by pet to draw their ire and I have a buffer to heal myself or re-mana if need be.
I try to use standard group logic with my pet, only I have to play dps AND healer while he plays tank. I keep him topped off because if I let him go and don't have the mana to toss a HoT when he needs it, we can both die. This has happened before and I wasn't happy about it... so I protect my furry adventuring buddy. I can always FD out of my aggro, he can't (I don't believe in cower). So sometimes it's best to LET things come and pick on me for a while as he heals or takes on multiple targets. I can always send the mobs back to him and if he's got high health, he can carry a heavier fighting load.