I also fire my cameras once every 3 months or at least once in half a year, if not in use. I go through all the shutter speeds and aperture setting. Do not forget to turn the focussing rings too, this keeps the lubricants in place and avoids the helicoids from getting stiff.
It very much depends on the camera, but this way you should be on the safe side. I have a Rolleiflex T that worked flawlessly but shutter speeds had become totally unusable when it had sat in the cupboard for two years. On the other hand, I once bought a plate camera and the shutter was spot on although not used for decades!