From: Chicago, Illinois
You are playing Axis, right?
In 1941, I would set Artillery units to 50 or 60% TOE, just until early 1942. This is because you will have an armaments crunch later in 41, and this will relieve some pressure.
Other than that, I don't monkey with TOEs. I do set all SS, and most Panzer, to REFIT to get priority for replacements.
Set any unit due to withdraw in 10 or less turns to 80% though; no sense wasting it (I say 80, because you need a bit of a cushion; without it, if the unit is JUST below 75%, it will spend a turn on REFIT beyond your control, sucking up replacements to 100% TOE)