In the slightly older days, before external instruments, the ability to mixdown (in realtime) with monitoring ON was great. You could mixdown your mix, without having to track in the external synths and samplers. (I used to run 3 fully loaded Akai S5000’s via a total of 6 ADAT lighpipes, plus about 4 other external devices on another bunch of lightpipes).
So the monitoring “stickiness” really was a “feature” back then. Imagine tracking all those instruments and then deciding to change the tempo!
And yet I mentally invented (and dreamed) about External Instruments (with auto compensating and permanent monitoring). The someone at SB had the same dream and external instruments are now the “norm”. Too late in a way, as plugins and LAN audio have taken over.
All this, of course, makes/made sense back then, only for a realtime mixdown. I take the point that you want it to auto switch out for a non-realtime mixdown.
Anyway - it’s not exactly “ancient” history, but sufficiently long ago for the logic of it to be forgotten. Also, it keeps you on your toes! (ie always check back a mixdown). (I am showing my age here…)