Ideally you should never run your shotgun out of ammunition, that way you’re only feeding from the bottom. The adage goes, “If you aren’t shooting, you should be reloading.” Try as you might, you’ll still get to the situation where the shotgun is now empty and the bolt is locked back. I throw a shell into the receiver and hit the bolt release. Then load the magazine tube. You don’t want to try to load the magazine first because the bolt will be locked back and the elevator won’t move to allow you to load shells. So you’d have more tasks involved to drop the bolt first. You are also at a disadvantage since the shotgun is unloaded at this point until you press the shell drop button, then rack the bolt to chamber the round.
Now if you have dangerous game around, burglars, lispy antifa queens and so on, you can’t get back into the fight immediately without going thru the manual of arms of hitting the shell drop, then racking the bolt. Sometimes loading get interrupted, so you might not get a full tube filled before you need the weapon again. Figure if the magazine was empty already, there was a reason. Follow the adage from above. If you fire two rounds, load two rounds if you can.
Like with a pistol, if you discharged 7 of you 15 rounds, you’d want to swap mags if possible if you have a moment.