Once you've been collecting music for a while, you will suffer from an abundance of riches: those 15 different versions of the Beethoven symphonies; those 5 complete sets of Bach cantatas; at some point, they will all become difficult to navigate and make playing any particular recording increasingly difficult.
It is for such times that an 'overflow' library is a good idea: a separate physical storage area on disk where you move your lesser-played recordings to as you come to realise that they aren't your favourite performances any more. They're still there on disk, though: so they can be restored from the overflow folder back into the main library if you change your mind later on! Or (more pertinently), they can be played at will whether they are considered 'overflow' or not. [...]