What part of the world do you live in? I hang a good portion of my guitars. I'm fortunate that living in southern Ca our weather is pretty consistent. I can let a guitar hang for a month and it will either be in tune or only a couple cents off.
I was born and raised in San Joaquine Valley. Now live in Midwest.
I learned to case my guitars after suffering a headstock break on an acoustic, back in the 80's.
I also found that keeping them cased, helped to save my setup work.
When I was gigging, I'd completely tech my guitars every week.
Including string change, cleaning, dismantling the bridge, soaking saddled in Windex and scrubbing, changing saddles as needed, polishing the frets, reassembling, checking neck relief, setting intonation.
Took a good portion of my Sunday, every week.
Occasionally I'd play an old guitar, that had been out of rotation. When I'd check the neck relief after pulling from the case. They'd be out by .002"-.003"
The guitar I played for most of the 90's, I ended up trading to a producer/friend. He liked to leave them out of the cases so he could see them.
After about 6 months I picked up my old guitar, that hadn't seen its case in as many months.
Neck relief was out by .027"
In my world, that's a mile.
So, as far as I'm concerned, leaving my guitars out, is the worst thing for them.