Hi Bernie,
I use the MP3 player to provide sequenceLIKE backings that I have created at home, and added backing cocals to. I made a Beach Boys Medley, for example that would be impossible to do live because the harmonies and the lead sing two distinct lines.
I also have a few comercial Karaoke tracks that I play over, that would be very difficult for me to reproduce with the arranger patterns. These are mostly horn section or guitar heavy songs.
I welcome any tool that allows me the freedom to express myself in song while I entertain an audience!