what it means:
and edit pane, where on can decide (tick visible/invisible), what he wants to see in the inspector and what not.
background:
there's several workflows and several tasks. i for one never need the track transpose entry on an instrument channel inspector - but i mandatorily need the track delay - so i always have the transpose in view, as the track delay is below that. now, the entire trackinspector is not big enough and there's a lot of space wasted, as the elements are very big (due to the touchscreen abilities) and one simply can't really make fit so one can see all info necessary.
being able to build inspector sets you prefer, you can set up the inspector to only show what you like to see when you wanna see it, using real estate in a way more effective way.