Can someone please explain to me, what this "feature" can help me with in my development work?
It looks like some kind of file commander, but it is not. Well, naturally, I googled it, and this documentation from JetBrains on IDEA Commander came up. From this, it seems that it is for mass copy, move, ... operations. Okay, cannot say I have missed it. Actually, I always start by assigning the Alt-2 keybinding to something else like Ant Build.
Are you using The Commander? Take the poll at right.