I think it’s a good idea to have some sort of check for each frame, however - I think it’s way harder to implement well, and may actually be bad for overall imaging if not done well… consider that sometimes there is motion in the scope/mount.. so while things might be in perfect focus, its possible a particular sub may turn out a bit blurry, in this case if it would trigger another focusing routine resulting in loss of at least 1 sub (180 sec) while it ran a pointless AF routine.
If it came down to a choice of per-sub check routines, I’d say that validating goto object is centered would come ahead of validating focus… unless someone could figure out a way it only triggers when really needed… maybe tie it to average total error for the sub to assess movement, i.e. only trigger if total error was under 0.75” which should produce a crisp star