is it dangerous to plug in the power/reset leads while computer is on?

I suppose everyone but me already knows what to do about this annoying little problem: the power leads on a desktop computer constantly falling out whenever some heavier cable is nudged. They're so loose, and have been loose on every motherboard I've owned, that I suppose they were designed to be loose. I finally took to plugging them back in while the computer is turned on. Is that supposed to be dangerous? My experience suggests not: I can't say I have received any shocks; nor does the computer appear to be damaged.

If I'm right that it's not particularly dangerous, would this be how everyone else handles the problem? Just plugging the leads right back in?