One reason is so I don't have to worry about different types of cables for a performance.
Worried about performance? You are going from stereo to a mono plug! You are intentionally trying to lose performance!
I cannot understand why you would not simply buy a cable to connect your rca's to your mono equipment. How would that lose quality? I mean, will you not have to use a cable to connect your modded jack to your equipment anyway?:confused: