Agreed with LAWriter. We rarely if ever get asked to mix music in 5.1. For advertising placements, we nearly always get asked for stems. When bouncing your final mixes, you should always bounce separate stems as well. (Drums only, bass only, guitar only, etc…). This availability has been make or break for licenses. We’ve gotten requests for music with the caveat “Only send me tracks that you have stems for.”
Secondly, in the off chance you need to revise or customize a track in 5 years and your session will no longer open on the latest OS, you can recreate the piece from the audio stems far more easily…
It’s a good habit to get into bouncing stems along with your final mixes. With offline bounce, it doesn’t take that much more time.
EK