I agree that using backing extends what is sonically possible. Take a look at the Depeche Mode 101 concert video. They use reel to reel players to fill out the songs, but, look up videos of Alan Wilder demoing how he played the various keyboard parts and you'll be amazed at how intricately he programmed those 88 keys so that he could play his synth parts live – all the fills that give those songs their character. On an early Kansas recording they also included some live recordings, and they played back the orchestra parts from a reel. It may have been "Sparks of the tempest" off the remastered "Point of know return". I think fans are sometimes disappointed when songs played live don't sound like they do on the CD. You also realise how hard it is to stay in time with pre-recorded elements when you play like this the first time. Take a look at this video where STS9 talk about how they sync live:
It'll blow your mind!