when freezers are not in use fr 2-3 weeks a month, should they be left plugged in?
Freezers have very little &quot;thermal inertia&quot; when empty -- the compressor cycles on and off more often (which can cause more wear) in an empty freezer than one that's full (or partially full) of food, which makes it less efficient:

A full refrigerator retains cold better than an empty one. If your
refrigerator is nearly empty, store water-filled containers inside.
The mass of cold items will enable the refrigerator to recover more
quickly after the door has been opened. On the other hand, don't
overfill it, since that will interfere with the circulation of cold
air inside. The simplest solution is to buy the right size for your
family in the first place.

Full/empty efficiency has also been answered over in Cooking.StackExchange.com:  Does keeping a fridge/freezer full significantly help energy efficiency?
I'd suggest not leaving the freezer empty when not in use, but keeping some frozen jugs of water in the freezer all of the time -- not only does this help reduce compressor cycling, but it also helps chill food faster when you load new food into the freezer.
Freezers in daily use can last decades, so I wouldn't worry about excess wear by keeping your freezers plugged in -- just don't leave them completely empty.
Fridigidaire recommends leaving their refrigerators on for periods of a few weeks, and turning them off for longer periods of time:

Leave the unit operating during vacations of less than three weeks. If the appliance will not be used for several months:

Remove all food and unplug the power cord.
Clean and dry the
interior thoroughly.
Leave the door open slightly, blocking it open
if necessary, to prevent odor and mold growth.


Kenmore has a similar recommendation for their chest freezers.