Many years ago when I actually used to fix these things we had the following procedure.

1. Aircraft stops
2. PB on
3. Chocks under wheels
4. PB off

Once the a/c was ready for departure PB back on. Chocks away and push back.

The reason for doing this was not because of brake pressure failing, it was for cooling purposes. A set of brake pads clamped to the hot disks caused that section to stay hotter for longer and could result in warping of the disks (that's what the manufacturers used to say 30+ years ago anyway).
In addition, once the system did cool down, everything contracted and the pressure of the pads on the disks decreased meaning there was a possibility of them no longer holding the aircraft still if on an incline.

I am sure with the introduction of carbon brakes etc these things have changed slightly but its probably good practice to follow this still.

Indeed. I worked for a similar outfit. Often I'd do the walk round and see a 1-2cm space between chock & wheel. Front steps extended. I asked the ground why the gap? "Because they become stuck under the wheel if we chock 'em too tight." So the a/c could roll enough to perhaps twist the steps. Captain at fault, naturally. Chocks were in.
And then we get the chestnut of SOP's that said 'Main Wheels' need to be chocked. Of course the agent who operates much on the right side of the a/c chocked only the right mains. Ok for me, but not for some. Then they started chocking just the nose wheel fore/aft, because that was by the headset for push back. OK for me, but not for all. You couldn't win.

In a vaguely similar incident, Falcon jet hits building....