Is there any practical difference between using Rig Volume versus Amp Volume? In other words, is one better than the other for any reason?
The only difference is where you load an effect which is volume sensitive (like compressor) after the Stack section. Try this as an experiement and you will see what I mean:
Select a Rig and load it into two slots of a Performance (to enable quick A/B comparisons)
Now make a major volume change (say +10db) to highlight what is happening. Make this change in Slot A with the Amp Volume and in Slot B with the Rig Volume. Save the changes.
Now add a compressor in FX Module X. Setting don't matter too much but make sure it is a fairly noticeable amount of compression to highlight the effect of the volume change. Save the performance again.
Play something and switch back and forth between the to Rigs. You should find that the Amp Volume boost doesn't get much louder as the compressor catches the volume boost and compresses it. Whereas, the Rig Volume version gets significantly louder as the volume boost happens at the end of the signal path after the compressor.
Not all FX are volume sensitive though. It is tempting to thing that the Delay or Reverb would get overloaded by turning up the Amp volume but this doesn't happen. If you put the same Delay in both Rig versions you will notice that the delay repeats sound the same in both cases.