Humidity regulates how much water it up takes. Dry air and the plant drinks more. With a humidity around 50%. The plant drinks slower. Slowing down the water up take to a balance where's the plant is happy. No fert burn at a given ppm.
It depends where you are in the world?
For me it's essential, my local ave humidity.
I couldn't be without a dehumidifier now it heats the tent cheaply and controls humidity.
Dehumidifiers are a crucial piece of gear honestly. Get one bigger than what you think you need and keep spares. This is what I do at least I keep an anden 320 and always keep a spare on hand in case one goes down. Each room has a dedicated dehumidifier.