[JRTJH]

If you add antifreeze to the plumbing lines, leave the water heater in bypass position. Antifreeze is corrosive to the water heater tank lining.

If you only use compressed air to remove water from the lines, there's no antifreeze, so it becomes a "personal choice".... Remember, however, that part of a "safe and effective de-winterization process" contains a step that says: "CHECK ALL PLUMBING FOR LEAKS BEFORE CLOSING UP ACCESS PANELS".... YMMV