I have got an Ibanez rack mounted hardware reverb. I believe it was made by Sony at the time. It can be put into either Mono or Stereo operation. In Mono panning the input signal has no effect on the output panning but the output is still in stereo.
In Stereo operation panning the input signal results in the reverb being panned as well. Not completely though. If I pan the input signal hard left for example I hear the reverb being panned too but it ends up mostly left and just a little on the right side. The stereo effect sounds slightly more pronounced as well.
It is more like how things would work out in a real world situation. If you had 4 musicians playing in a room and they were all positioned across the room for example and only the most left player were playing you would still hear reverb right across the room with most of it being on the left side but there would still be some all be it lower reverb on the right side. It would not be the case that
MIke has outlined where there would only be reverb on one side only. That cannot really happen in the real world can it. My Ibanez reverb has obviously got things set up to replicate what happens in a more real life situation and it sounds good too.
I believe this is more likely the way it should be. It is nice because if you have say 4 input sources that are panned hard left, say 10 O clock, 2 O clock and hard right the reverb comes out that way too. You can hear the hard panned instruments reverb on their respective sides etc.
It depends on what you want to do. Sometimes the mono in stereo out reverb effect is the better option and other times full stereo sounds better to me.