Honestly, I don't usually chock the trucks when I've got it parked on flat ground or just idling unless at an event. I do try to always chock it when pumping or on any hill.
May I direct your attention here:
Older automatic slack adjusters have a tendency for the grease to harden, preventing the automatic adjustment. You should be doing a periodic check of parking brake application on your daily or monthly check. With regard to aerial devices... Our policy is to chock the wheel/s that are in contact with the ground. I know some aerials raise all wheels of the ground, but as a matter of course, at least one wheel should be in contact with the ground. Operating on grades of more than 3% will result in movement of the entire aerial down slope in snow or ice conditions. Set-up in these cases needs to have the snow removed, and anti skid sand (NO SALT) placed beneathe the out-riggers prior to setting up the aerial. Chocking the low wheels adds safety to a tenuous condition. Ground operator needs to periodically check the condition of the chock and outrigger down pressure while operating. From experience having an 80,000 lb platform slowly "SKATING" down hill while you are operating is a little scairy.
Wheel chocks are manditory. They are NFPA but that is just a suggestion. I'm sure someone has an osha rule somewhere.
The next question is how tall a chock to use. We have several older chocks that are only like 6" tall and some newer ones that are folding and about 12" tall. I think if your tires are 12-22.5 you need at least a 12" chock to meet the standard of DOT. (10% grade fully loaded truck or whatever) These chocks are over $200 each. The 6" units are easy to handle and only run about $65!
Good luck with that!
MHO, the rigs should always be chocked when out of the station. The agency I work for has that as a policy, sometimes I have to remind the driver/operator, but all the engineer's are in the habit.