I leave mine outside.

I figure it does less damage than subjecting the thing to the stresses of high temperature changes. From 30 below to 70 degrees ain't good for anything. If there's precipitation I throw a tarp over it.
There's salt on the roads and I figure it has less chance of doing damage to the bike if it's in the freezing cold. Washing it off is not an option where I live, unless I went outside with a pail of hot water and soap.....that ain't going to happen, because....

....It takes me 30 minutes to prep for a ride (getting all the winter gear on, the toe-warmers, the boots etc), then I have to load everything in the car and drive, then unload, ride, re-load, drive....
When I get home it's usually dark, my feet are frozen and my body/core wet and cold. It's not time to be messing with the fat bike. So she sits outside and if she moans I just beat her with a stick.

I used to bring it in the house. I had a tarp and sat the wheels on newspaper to catch the drain-off.

Time will tell what works best.

Whatever it costs me in depreciation is money I can offset with the gym membership that I don't have, and the medical expenses that I don't have, and the seasonal anxiety...and...and...