omissis
It doesn't delete gauges based on when they were last used. It automatically scans all of your aircraft panel .cfg's and then scans the gauges folder to see if there are any that aren't mentioned in the .cfg's (meaning that they aren't used by any panels) It then moves the gauges to another folder names 'Old gauges' meaning that if it has accidentally removed any used gauges, you can simply copy them back over again into your regular gauges folder! Simple! ;D
Not to steal your thunder nor to demean your software (far from me), but Drgauge does the very same thing. Scans the Panels and makes backup of the gauges removed. :-?
At least the Drgauge I use, does it.

Of course, if you have a bad experience with Drgauge, then use another software.
