This short detailing tips aims to educate you on two reasons that should really help prove the case for always chocking your airplane, even if it's just doing routine cleaning.
Why should I chock my airplane when Cleaning
Prevent your aircraft from rolling into another aircraft
Unless you are extremely fortunate, it is likely that your aircraft is being kept outside, or you are in a tight hangar with other aircraft, tool boxes, and whatever else in close proximity. I know that I've seen this first hand in our hangar where you have a maximum of 12 inches from one aircraft to another. If you're not careful, it is so easy to lean in a little too hard and cause the airplane to roll into another. That is NOT a fun day!
Save Your Body
I personally experienced the threat of this one. When cleaning and polishing the tops of the wings, it's really tempting to extend your reach a little further than comfortable. This becomes a big problem when you are standing on the top rung of the ladder and the airplane begins moving backwards. Two takeaways here: 1) Chock the airplane so it cannot move, and 2) Take your time, and move the ladder!
I used to work at a flying club, and first hand saw an older gentlemen accidentally push his aircraft back and fell when fuelling on top of the wings. Luckily he was alright.
Take the extra 30 seconds to place a chock firmly under the main wheels to prevent bodily injury, and a hefty injury to your wallet. It's so simple, but can make a huge difference!