It's helpful to fade out specific Instrument(s) by automating the gain on a plugin. This method doesn't lock up the volume faders with automation values, so the track volume can still be adjusted for mixing with ease.
This works really well with Pro Tools' 'Trim' plugin, because its gain option goes all the way down to -Inf dB; however, S1's Mixtool only goes down to -24 dB!
This might be enough for gain staging, but not for other tasks. Please allow larger gain reduction values with the Mixtool (e.g. -94 / -Inf).
PS: Yes, I know the above use case can be done by putting a fade-out on the event too, but not for MIDI Instruments.