Either DE in the 3-4 sets or DT in the 4-3 nickel sets or both.
I think we picked him up in FA to give us options because we didn't have any proven 3-4 DEs. Both Urban and Watkins were picked up with that in mind. However, we drafted Odighizuwa, who even though he doesn't have ideal size, has those long arms and strong ability against the run, so if he's ready, I think he's got a good chance of being out there with Urban as essentially 3-4 DEs (although in the hybrid base, Osa would be considered a 3-tech, I believe, and Urban a 5-tech.)
If that's the case, then Watkins has to work himself into the rotation as a pass-rushing DT. That might not be hard for him to do because Urban isn't a pass rusher, if Osa is going to be one it might take a while, Gallimore (the best bet to be at one of the DT spots in the nickel IMO) is still development and I don't hold out much hope for Hill. Watkins' top competition for an inside spot in the nickel fronts might be Golston.
Watkins is our safety net because we know he can play in the league, even if he's the type (like a Tyrone Crawford) who can hold down a position when you don't have better. If Hill and Gallimore both step up, he might not make the roster, although he might be counted on as a 3-4 DE if Osa isn't ready. However, he also could be the reason Hill doesn't make the roster if Hill continues to be only worth a flash or two. (Right now, Watkins is the better player and probably should be considered better than Gallimore, but likely only because we've only seen Gallimore as a rookie.)
I view Urban as a player we picked up to definitely be a starter as a 3-4 end. Watkins would be more of a starter by default.