There have been many theories that have speculated that Bloodbending could have positive benefits. It'd likely be used for medical purposes.

However, I doubt any Bloodbender could bend Red or White Blood cells directly. They'd be too small.

I once created a fanfiction story concept for a community of waterbenders trying to study and use bloodbending in a positive way, much to the dismay of the world at large after the devastation Amon (and others) unleashed during the life of Korra. Eventually, this lead to my next Avatar's waterbending companion being a member of this community while hiding his identity for most of the story.

As for the OP, there would be a lot of practical uses. For example, a part of CPR is keeping the blood flowing through the heart, so having a medically trained bloodbender for a bumpy hospital ride would be very helpful. As for the blood cells themselves, I don't think so. To me, that'd be like saying a waterbender focuses on the bonds between Hydrogen and Oxygen, per se.