I'd say about a third--maybe more--of the guitars I see still have the silica gel bag inside from the factory. I leave them in there, as I assume that's what the customer thinks best, but not sure what actually is best practice in this regard? Thoughts?
Are you talking about the small packages (~1"x 2") of silica gel beads? They are a desiccant meant to prevent mold/musty conditions while being shipped in closed up case inside a shipping container on the ocean in very humid conditions. They would not provide anything in terms of humidity control in an open air situation. I usually toss them in the case accessory compartment to help with mustiness from over humidification which is an issue for more than half the year where I live in the SE US.
They only absorb so much moisture, then are no longer useful unless dried out. Weigh one wet and then dry - I doubt it holds more than a teaspoon of water. To leave them for years inside a guitar or case is useless after they are full, unless you dry them.
here on the mid-atlantic coast i say ditch 'em.
in summertime it's humid but not insane humid (guitars are generally happy indoors where even with air conditioning it's usually in the 50% ballpark) while our winters are dangerously dry, so those packs either do nothing (summer) or are possibly harmful (winter).
With 35 yrs. in music stores I've always chucked them but keep the larger one for my repair shop and garage tool boxes (drawers). Don't forget. People eat Tide Pods.;)
Those silica packs are generally put in there by the case maker to absorb any moisture from manufacturing and during their boat ride from the orient. By the time the guitar reaches a store they have done all they're going to do. Chuck them in the trash.
I save mine to give out to the trick or treaters. ;)
I've been saving them, but I'm honestly not sure why.
Planet Waves make a humidifier/dehumidifier kit, all in one. Not certain how effective it is because I live on the coast of British Columbia and my home humidity reads 40 to 47 per cent which is about ideal.