At the BIG oil company we had computers everywhere and they all had air filters installed on them. The clean-up crew would pull the filters and run the vac hose over them while they were cleaning the carpet. This took place five days a week.

The head of our communications dept had the title of Wire Chief. The Wire Chief would hold a small class now and then on the care and feeding of communication equipment, and he pointed out that dust will not really hurt radios or computers. BUT... dust will attract water vapor and that would have a terrible effect on the equipment. The only way to keep the water vapor to a minimum was to keep the dust to a minimum.

This is also a reason not to use unfiltered compressed air. It is easy to attach an air filter with a water knock-out on the outlet of your compressor. Cheap, too. All air has water vapor in it unless you live in the middle of the Gobi, so if you are spraying your computer with untreated air you are also spraying it with small amount of water vapor.

That's why the cans of compressed air are really the best thing to use.

By the way, many of the cans of 'air' are really cans of compressed Ethane, so don't smoke when you use one of these.