Brake Cooling..
It's a well known fact that brakes cool better when they are released. If the brakes are set, the disks are squeezed together as a single unit. If the brakes are released, air is allowed to circulate between the disks and will allow for a quicker dissipation of heat.
As for properly putting chocks in place....there is no way of seeing it from the cockpit. If the airplane begins to roll...common sense says they werent put in correctly.