Again, SORRY - found what I thought had been deleted, here's what is germane to this topic/thread:

+ when writing original music, I use iReal to keep track of the chord changes, form, & to try out diff. rhythm patterns & tempi.

+ I've used iReal to write up a background track for a song at church, when I couldn't find a background track available to purchase. I've even written up a quick track (if it was a simple song) in the morning before church & used it in that morning's service.

+ for more involved arrangements, I've used iReal to lay out the basics of the arrangement, & exported the track as a Midi file, & then imported the Midi file into Logic Pro on my Mac for further work, additional instr. parts, etc.