I buckle my top two buckles if they're not going to be used for a while. I do it out of habit but I'm not sure how much of a difference it should make to the calf area. I don't buckle the bottom cable. I also think how they are stored (particularly the temperature) might make a difference, and here's why:
Ski boots are plastic (duh) which means that they will try and revert back to their stress free state. This will be close to the the shape the boot was originally moulded too. How close to the original moulded shape of the boot this stress free state is depends on the processing conditions of the boot. Assuming that the the process engineers did a reasonably competent job they should be little residual stress from the moulding so the boot should stay pretty much its original shape. This should mean that the boots don't need to be buckled as the plastic will stick to its as moulded state whether you buckle them or not.
However, if you've had your boots modified (i.e the toe box punched out etc...) then the boot plastic will try and revert back closer to the shape they originally came in. The speed at which this will happen depends on the type of plastic (along with any additives too it) and temperature the boot is at. Depending on the boot this may mean that if a boot is stored somewhere warm your blown out toe box may contract back towards its original shape so after a summer your toebox may seem tighter than last season. If you crank down on your toe box buckle/cable then this will likely speed up this process (which is why I don't buckle my toe box cables).
If you've ever left a credit card in your pocket and put it in a hot wash the card will come out warped and bent, you can fix this (and get an idea of why ski boot plastics can change shape). You can get it back to it stress free state (which is pretty close to the way it was supplied, i.e. flat) by just putting it in boiling water and then letting it and the water slowly cool down (if one side cools down faster than the other it will warp the card).