Re: When to detune strings?
I only detune when changing strings or shipping an instrument.
Re: When to detune strings?
If I let an instrument sit for a long period of time I may detune slightly, but usually simply look in on it every couple of months.
Re: When to detune strings?
I would think not. Mandolins are designed to perform with the string tension in play (so to speak) and a well-constructed instrument should be just fine even when not being played. I am often astonished when I check the tuning before a gig and find it is still in tune after having been in the case for a few days or a week or even more. Of course, every instrument is different, so YMMV.
Re: When to detune strings?
Generally - never; unless I was shipping it somewhere or possibly checking it in for a flight.