Some years ago, I recall meeting up with some friends who, along with myself, share an intrinsic love for automobiles. In our stimulating discussion about car quirkiness, my obsessive and somewhat eccentric nature led to the topic of why I never fold my side mirrors whenever I park. They questioned my logic and, of course, I was more than happy to explain. The habit may be a bit odd at first, but let me shed some sense on this practice.
I've been pretty anal about car maintenance ever since the automobile bug bit me years ago. I guess it was a recessive gene that eventually surfaced, as my late father was a true-blue petrolhead.
Here's the explanation: Most vehicle blemishes such as dings, dents, and scratches accumulate around the front, rear, and side panels. Sometimes, the roof too. Why? Well, these areas come in contact with, well, almost everything and everyone your vehicle comes across whether you're moving or stationary.
There's nothing more irritating than returning to your car to find damage that wasn't there an hour ago, when you parked it in a supposedly safe area. No place is absolutely safe. It is truly up to the vehicle's owner to find ways of improving their vehicle's safety regardless of location. With that in mind, I developed the habit of never folding my side mirrors. Even the home garage is no exception. Simple observation led me to this habit that definitely suits our motoring environment.
Folding your side-mirrors eliminates/lessens that buffer zone of safety between your side panels and pedestrians passing by your parked car, or that vehicle parking into that vacant slot next to your ride. Based on experience and how the human brain reacts, regardless of how small you think your side mirrors are, we are always subconsciously/consciously avoiding to hit it.
Your mirrors lessen the odds of a person who may be holding, say, an umbrella, carrying a bag with zippers/rivets sticking out, wearing jewelry, etc., coming into contact with your car's sides. In the instance where someone or something hits your side mirrors, the damage it may incur (which usually is very minor) can't be as costly or bad as repairing dented and scratched side panels, unless that person or thing decides to intentionally break off your side mirror. That would be considered vandalism/theft and is off-topic.
To put things into proper perspective, the whole idea here is preserving your factory finish. If your car has one of those special colors that's difficult to match by any paint shop, I highly suggest exerting extra effort in maintaining it. Keep in mind that no matter how small the scratch or chip on your finish is, it will require refinishing the entire panel for an even result.
As a bonus, let me share with you another technique I use incorporating my side mirrors given we have a lot of cramped parking spaces. When parking next to a vehicle, especially one with long doors, align your side mirror to where that door's handle is or simply estimate the trajectory of the same door if it's to open and hit your car. Better to have that door's edge hitting your side mirror than messing up your door panel.
When sandwiched between two cars, focus more on the passenger's side of the other car. Usually, drivers tend to exert more caution when opening his/her door rather than a passenger like a little kid would. At the end of the day, applying common sense and a bit of imagination will definitely improve your chances of preserving the beauty of your car.