Humidifier/De-humidifier for music room?

I keep a lot of musical instruments in a small 'music room'(Aichi-ken, city not country).

Up to now, I've been running a DE-humidifier all year round to protect them (guitars, etc) from the climate. I've used this, figuring Japan is humid, so de-humidify. Constant setting shows around 48-50%.

However, I see music stores with humidifiers going 24/7 and don't recall seeing dehumidifiers much.

Have I got it wrong?

Question: Should I be using only dehumidifier or only humidifier, or both or either depending on the time of year?

Very confusing, so advice much appreciated.

Also, I've heard that some humidifiers can leave a kind of white dust/powder. Any recommendations on a model that doesn't would be great. Thanks!

Japan is mostly very dry in winter, so many people would switch to a humidifier to maintain a constant humidity. Then in summer a dehumidifier is definitely needed. A dehumidifier in winter would seem like a waste of electricity unless there is a source of humidity, like a shower room, nearby. Do you have a hygrometer which tells you what the humidity actually is so you can judge which is needed at a certain time?

I suggest you ask this question on a music-related site rather than here-other countries have similar weather patterns to Japan as the humid summer/dry winter pattern is quite common, and you are more likely to get answers from people who know about musical instruments.