Well, on the (planetside) battlefield, sometimes your fellow soldiers will get horribly maimed and/or mangled. Yamataians and NH-29 Nekos can (slowly) self-heal minor to medium flesh wounds, but having nanites in your blood doesn't help too much when, say, you just got your legs blew off.
(A NH-17 is much more, let's say, robust. But we're trying to tone down power levels and phase them out.)
The job of a medic, then, is to make sure that the victim survives until she can be evacuated. Sure, we can almost always bring her back via ST if she dies, but it's an emotionally and physically painful process for many, with a much longer recovery period.
So, no, a medic doesn't have to worry about first aid in the sense that there's no...