As I have been converting my vinyl and CDs and also buying digital copies of tracks, my library is getting larger and am looking for a way to add tracks to a "current playlist" (or tracks that you play currently in your sets). When this setting is enabled (or box ticked) for the highlighted track, it gets added into the "current playlist". What then happens is that there is a toggle somewhere on the screen that just shows the tracks in the playlist. This playlist filter is applied to all crates, sub-crates and smart crates automatically if the toggle is on.

The reason why the creating a smart crate with tracks added within the last few months would not work as sometimes people like to play classic tracks that may have been added a long time ago.

It is handy as you just apply the setting to the track once rather than creating several extra crates (in my case, sometimes I play by genre, sometimes I use a smart crate that groups the BPM to a much narrower group) and thus is much easier to manage.