This is an insert cable, generally used for audio consoles or other preamps that have a send/return on the tip/ring of a 1/4inch TRS jack. It's a way to insert a component (like a compressor, EQ, etc.) directly inline with a preamp by using a single 1/4inch jack.
This "Insert" cable intended primarily for mixing/effects insertion applications, but it also can be used as a "Stereo Breakout Cable" since it is wired exactly the same way as a stereo breakout cable.This cable can also be used to split an unbalanced stereo signal into two unbalanced mono signals,