A really humid garage can cause rust to form on bare steel parts in a short amount of time. I realize that a bike will experience humidity outdoors but if you bring it inside that limits the effect, where as if you keep it in a garage it is exposed 100% of the time. Unless you have a climate controlled garage, in which case you are a gangster.
I know my bike won't melt if I ride it in the rain but thanks for letting me in on your "trade secret". My wife doesn't care if I make a little mess. And I definitely bring my bike inside after I ride it in the rain so I can thoroughly clean it off.
I'm just saying that unless space is really limited, or your wife doesn't allow you, there's no reason not to bring your bike inside.
I live in PNW -- it rains most of the year here, and the relative humidity is high during the rainy season (which is basically Oct-June). If you bring your bike in the house, you will track mud everywhere.
The last bike I sold (steel) had about 60,000 miles on it. I got 1/2 of what I paid for it brand new and got 10 calls within the first 24 hrs of listing it on CL (I gave it to the first caller). My current workhorse bike is steel. It gets wet all the time, I never dry it, and it lives in the garage. The amount of rust I get is minuscule -- certainly nothing worth worrying about.