Collection Tree allow you to have mass manage tool between your collections.

with right click on collections or set :

Open

view the selected the sets or collection in Searching cards panel

Alert

Add selection in alerts module to Monitoring cards

Mass Movement

manage massive moves between collections (launch could be long if collection is huge).

Missing cards

alows you to add missing cards in selected Collection/Set. For exemple if you have cards #1 and #4 in selection, you will add #2 and #3. It could be interesting , if you manage a "Needed" collection.

inter collection cleaning

alows you to remove in current collection/set, the cards already present in another collection.

Sets move

move all cards present in selected sets to another collection