It seems to me that bloodbending can be a useful healing tool. Internal bleeding, rapid blood loss from a battle wound... all things that can be better controlled with bloodbending.
It'd be for blood-specific issues. Thinning out blood in blood clots and hardened arteries... Stopping blood flow in cases of internal and external bleeding.
I just think it would be neat for Katara to use the ability in a positive way, given how it was introduced.
She might have been able to save Jet, but I think the time required to get him on his feet was prohibitive. As we saw in "Day of Black Sun" you don't get insta-healing from Waterbending healing abilities. We even saw that the people Katara was treating in "The Drill" from Ty Lee's chi-blocking techniques weren't on their feet immediately.
Plus, Longshot told them to go. If he was talking, you KNOW it had to be serious .
Anyway, I think that Waterbending healing techniques are related to bloodbending, but not quite the same. Healing is used to return the body to a state of balance when an injury knocks it out of balance. Bloodbending takes an otherwise healthy body in a state of balance and deliberately knocks it out of balance for the bender's own purposes. I suspect that the fundamental techniques used are the same. It's just the purpose that's different.
I think Hordesman is right that it might be usable to close wounds faster or deal with internal bleeding or hemorrhaging, but given the constraints imposed by BS&P, I don't think we're ever going to see it used that explicitly. The most we've ever seen of blood on the show is the occasional minor cut. It would be cool, though.