Cycles of removing crank arms will not hurt anything. Yes, doing it frequently creates opportunity for error. Done correctly the procedure can be repeated as often as required, even if imagination decides it must be done constantly.

fietsbob has correct point about letting condensation vent. Plenty of other ways water gets inside frames. If no hole in BB the only alternate vent is an open top seatpost, which doesn't work as well and which almost no one has any longer. No vent at all and steel frames will rust.

No effective cleaning could possibly be done by flushing bearings in position. It is just not hard to do the service the usual way.