Shut off vents in rooms not in use?
Noticed that the second floor, during heating season is too warm and the
first floor is too cold?
Shut off vents on the second floor to force more heat to the lower floor,
and to reduce the over heated second floor?
Desired more cooling in a room with a large solar exposed glass area
while all other rooms were cooling comfortably?
Found yourself constantly fiddling with the thermostat or using space
heaters in some areas?
Found that the guest bedroom is too cold for your visiting mother in law?