As in cold weather operation there is a risk of movement being impaired due to the (re)freezing of contaminants, the freedom of movement check makes a lot of sense.
Considering the checklist is done regardless if the aircraft landed 30 minutes ago or 30 hours, it is very sensible to do this. Contaminants could have accumulated in many cavities, including the flap fairings, either due landing on a contaminated runway, taxiing in on a contaminated taxiway, or due (winter) precipitation/deposits being washed off by deicing fluids. Why not ensure these vital flight controls have the ability to move freely, same for ailerons, rudder and elevator.