If you are just mixing BB tracks then 16bit is what you can leave them as.
If you want to add vocals or other instruments then the session will be at a higher resolution.
BB needs this feature for the Biab Plugin so it can render tracks at the same resolution for the BB Plugin as to what the DAW is set to, so when it sync plays back the generated rendered wav files in the local folders, then when you drag them into the DAW it's not having to up sample them and have another copy.