When I was growing up, "humidity" was one of those things that was considered an undesirable thing. It made heat hotter and cold colder. It turned days that were just "warm" into miserable, muggy, don't-want-to-move days.
When I first moved to Denver, one of the things I enjoyed was the lack of humidity in this essentially desert climate. Hot summer days were bearable with just a fan. Opening a window was a viable option. Clothes could actually drip-dry. Even my naturally oily and acne-ridden skin started to clear up for the first time in my life.
When my dad got us a deal on a new furnace for our home (he was working in the industry at the time, so it was a good time to buy), I was somewhat bemused as to the existance of the option of a "whole-house humidifier". Why on earth would you want to add humidity to your house? My wife, on the other hand, a Utah native (where they also have a fairly dry climate) and owner of naturally dry skin, was very excited by this attachment, though.
After a couple seasons, I've gotten to understand this concept. The winter can get very dry, especially with the heater running as much as it does to keep the interior of the house above freezing. The extremely dry air ends up being very uncomfortable — it feels like you're living in a desert. Plus, there's an awful lot of static electricity that builds up in everything. The humidifier helps to make it more comfortable. It also makes it feel a little warmer, and it has the nice side effect of lowering static potential.
This winter has been especially bad. The power outlet attached to the furnace is dead. This outlet is powered by the furnace, so that it's on when the fan is on and off when it's off. So the humidifier hasn't had any power. I hadn't made getting that repaired a priority.
Then I noticed the problems. First, my shoulders would itch terribly. Yes, I, the one with the oily skin, had to start putting greasy gel on my shoulders to moisturize them after my shower in the morning. Then, my throat felt sore, the dry, parched sore of eating sand for two weeks. No matter how much water I drank, it always felt dry, and I would wake up in the morning feeling like it was on fire.
Then my oldest son started having the same throat issues. And my youngest was having trouble breathing at night. My wife broke out the portable cool mist humidifier, and that helped the toddler immediately.
That pretty much decided my course of action. Last night, when I got home from work, I ran an extension cord from a working power outlet to the humidifier. Since we run the fan full-time, it doesn't need to switch on and off, so that wasn't a concern. (That's a trick my dad taught me — if you set the "Fan" switch on your thermostat from "Auto" to "On", it runs the fan continuously instead of just when the heater or A/C is running. This keeps the air in the house circulating and at an even temperature, so you don't have the upstairs at 75° and the main floor at 65° and the furnace still burning fuel because the thermostat set at 70° is on the main floor. You do have to clean the air filter more often, but ours are the metal kind you vacuum out and reuse instead of disposable.)
I then had to run to Home Depot to get a new pad for the humidifier, since the old one from last year was scaly and wouldn't hold water (they're only $12 and typically last a winter season). Switched it on and set the humidity level to 20% (the markings have a recommended level based on outside temperature, but I've found that a constant 20% works ok, even if it means the windows occasionally show a layer of condensation on the really really cold days), checked for leaks, and closed it up.
Already, I can tell a difference. I woke up this morning and my throat didn't feel like it was full of sand.
Still, if you had told me a decade ago, before I had moved to Denver, that I would be voluntarily adding humidity to my own home, I would've laughed in your face.
Interesting side note: before we got air conditioning, we would cool our home with evaporative cooling fans. They actually work on the same general principle as the humidifier — a pump pumps water into a pad, and a fan blows across it. The cooling comes from the water evaporating. They actually work quite well in this climate, where water actually evaporates. I hadn't ever seen them before, which isn't surprising, since I had lived in places where it was more common to see water spontaneously condense out of the oversaturated air than evaporate into it.