Muting or fading portions of regions in GB without affecting the track.

No. When you use the automation on the track to lower the volume to zero at the end of the region of the guitar part, it lowers the volume on the whole track, including whatever effects (delay and reverb) that might continue to play (to be heard).

Doing it this way, in effect, mutes the track. In other DAWs you can put a fade on the region itself while not affecting anything else in that track.

Another way to explain is this: on a mixing console I could pull the fader down on the instrument track without pulling the fader down on the aux where the effect resides.