Someone pointed out that when you turn the keyboard upside down and shake, dust etc. can fall into the hollows of the keycaps. When you turn it right side up, that dust can fall into the switch mechanism. It's hard to say if the risk outweighs the benefits, but I generally avoid doing it now. I seem to get very little build-up anyway, so I can get away with a proper cleaning every 3 to 6 months.
Prevention is better than cure, so I use a soft brush to flick dust off my keyboard when I notice it. If I notice grease building up on the sides of the keys I wipe it off carefully with a cloth so it doesn't fall in.
A spill-proof coffee cup is a must for me. I drink it constantly, so the odds are against me if I don't eliminate the risk, LOL.
I have mini attachments for a vacuum cleaner that I could use to clean keyboards, but it would be overkill (and I hate the noise.) USB vacuums on the other hand seem like silly toys. One day I'll find a sensible compact vacuum for the job.