As an engineer of xx years, I do what the pilot asks me to do
If (s)he tells me (s)he is going to release the brakes, I put the chocks in a little tighter on the downhill side. The pilot will probably freak out if the aircraft rolls more than an inch or two (onto loose chocks). Once the aircraft has settled onto the chocks, even if the park brake is reset later, it's basically impossible to get the chocks out again, especially after refuelling. Having said that, it's no sweat off our noses to tow the aircraft a few inches forward to get weight off the chocks to remove them.
It matters not a jot if the main system hyd pressure drops to zero overnight, the brakes remain ON.
We would never rely solely on the park brake for parking an aircraft. The Boeing 744 maintenance manual only specifies 8 hours of braking ...and then only if the (any) of the following tests are done:
Accumulator pressure drop of less than
1) 275psi over 10 minutes
2) 600psi over 30 minutes
3) 800 psi over 1 hour
4) 1000psi over 2 hours
But then there is always Murphy's Law
The park brake relies on the principle of trapped fluid in the brake lines (but there lots of valves through which fluid can leak if seals are faulty).
We leave the park brake set at all times (unless the brakes are hot) and the wheels chocked. Our standard towing/pushing procedure is always to ask the flight deck to release the park brake or to confirm that the park brake has been released.
Rgds.
NSEU