Two main things:
The ability to hide individual notes/lanes. Ideally, not just in a map (ie. unmapped notes), but also in very complex kits, like Toontrack’s Superior Drummer kits, the ability to simply hide articulations or kit pieces you’re not using. Studio One does this nicely.
1.1) alternatively, the ability to collapse articulations, like Superior Drummer 3’s internal grid editor.
Ability to color code notes/lanes, eg. Green for snare articulations, purple for kick, blue for hi-hats, etc. Studio one also does this nicely.