Okay, so I don't know everything about the career. But in a nutshell...
My source for your comedic pleasure.
"I do a h*** of a lot more than just "assist" the pilot, especially in air-land missions. I make sure we're on time, on target, safe from threats and within airspace boundaries. I calculate turn timing so we don't run into other aircraft in formations. I determine where we should be and how we are going to get there when we do an airdrop. I call the drop. When someone starts shooting at us, I deploy the chaff and flares and help call the evasive maneuvering. Navs do the "higher thinking" (math and related problems) so the pilot can get the plane where it needs to be. In high level, there is a lot less for me to do, but I'm primarily responsible for making sure we're not tooling off into the middle of nowhere. I keep track of the navigation equipment to keep track of malfunctions. If the INS or GPS goes tango uniform, I bust out the magic tricks that keep us on course. I monitor fuel levels. I do the route planning. If we have to divert, I figure our new course. Of course, most of what I've described is what we do in the C-130 world, one of the last places where the nav can run the show, but it should give you a pretty good idea of what the career field is all about."