Detune or Not Detune.

If I were packing my guitar away for 3 to 6 months or longer, yes, I'd detune it.  Probably a full step, so down to D standard and I'd put a couple of humidity packs in there with it.  No point in the guitar having that full stress on it for no reason.  The detuning would keep enough stress on it so the wood doesn't settle in a way that you don't want, but not so much that leaving it by itself for such a long period of time would have any detrimental effects on it.

When I put a guitar away for the winter I detune 3-4 turns, probably about a full step. The amount isn't important. Detuning further isn't going to hurt the guitar. I have a few guitars that haven't had strings in them in a few years. I really should work on them some day.

I also put a home made humidity pack in the guitar. It is a quart size zip lock bag with 3-4 holes poked through it with a screw, and half a sponge, fully saturated and wrung out a bit. A saturated sponge that doesn't drip may seem OK, but when you push the back through the sound hole it will compress and water will get into the bag with holes, possibly leaking into the guitar.

The humidity pack is inserted mostly into the guitar on the bass side, leaving the zip lock part out of the sound hole. A gallon size zip lock bag is slid under the strings and covers the sound hole. Then the guitar is locking into the case.

Derick,TonyKgull,ladyssolo,CTGull,Greg Ballantyne,
This is what I was hoping to hear.
No one has said they have had a bad experience from leaving there guitar tuned.
When you think about it if you have the same guitar for years, you would have had it tuned up continually, with no effect, we hope.

Detuning and retuning every use would certainly cause the G strings to break after 4 or 5 uses.

Use Elixir strings and you won't have to change the strings for a year or more, depending on how much you use it.

I wouldn't worry about detuning an electric guitar. The solid body isn't going anywhere. It's the string tension causing the top of a flat top guitar that causes it to warp over time.