My thought on this if you can flex out a boot. i mean wear it out by fatiguing the plastic then the less times you bend it the longer they will serve you. This puts me in the loose buckle camp.
I spend a lot of time in boots so I often do low level lessons unbuckled because walking, standing , bending is involved.
From the parking lot I only wear boots if I'm late, parked close and the lot is covered in snow. Otherwise the only sane method is with a sole cover. I test drove a pair of Yakitraks and they were actually fun to walk with . They went on easier than Trax and felt like risers when you walked in them . Nice foot hold, easy to get on and on hard surfaces kind of bouncy.
Soooo. Unbuckled, let the foot move and protect the soles .