Just stated playing with the Slice Transform effect. Nice!
It doesn't seem appropriate for it to show fullscreen when there are no active slices (except for case when Scaling is set to Mask). This includes when no slices are in the list, when all slices in the list have the Bypass option selected, and when you Solo a slice that has the Bypass option selected.
Example:
Create a bunch of slices that represent musical notes.
Add the "note" slices to the Slice Transform.
For each slice, MIDI map the Bypass option to Piano mode with Invert.
Now when you play your keyboard (or have some other MIDI notes input, eg from a sequencer, DAW, etc) then the "notes" on screen are activated. Unfortunately if no notes are pressed, then all notes are shown (the whole layer/comp).