Dangerous and not cost effective either.
If you fold the mirror only 75 times a day and it takes only 1 second to pull it in and 1 second to push it out, that is 150 seconds or 2 1/2 minutes.
The center I drive in puts approximately 80 routes on the road daily(it's a big center). 80x2 1/2= 200 min a day or 3 1/3 hours a day.
At the overtime rate of approximately $50/hr that comes to $167/day or $835/week.
$835 a week to POSSIBLY save a $7 mirror?
In only 27 years of driving I've never had a mirror hit while parked but I expect it could happen any minute
.
I'm frankly surprised that UPS doesn't FORBID us to fold the mirror in.