I am using Return 3/4 for practicing with Drum Machines or Backing Tracks. I placed the corresponding FX stereo Loop in stereo FX 3. In FX4 I got a natural reverb to glue drums and guitar together. Sounds way more pleasing. The AUX return doesnt do that trick.
Now we got USB recording. Whenever I got a good idea for a new song while jamming, I would like to hit RECORD and be able to record the guitar stack in addition to the dry drums hooked to Return 3/4 separately. This way those prints could well be used for a final song. And for monitoring only there is still some reverb ear candy...