Tap tempo isn't a feature I use, but my expectations would be that:
- It is a temporary tempo setting,
- Just for that song,
- Just for that iteration/instance (i.e. until you change to another song, and then it is lost)
- If there is a tempo stored in the Song Details, it does not over-write/update that field. If you want to permanently update the tempo of a song, then go and update the Song BPM field.
But I guess we all have differrent assumptions and expectations based on previous experiences, so mine might be different to other people's.
Insofar as the location of the tap tempo button on the mixer, it seems quite 'out of the way' to me (at least based on Build 1876 UI) from the perspective of being concerned about accidently hitting it. In fact, I was half-expecting to see people who regularly use it wanting it to be available somewhere on the main UI, e.g. available as an Assignable Button (which it doesn't seem to be?).