We bought a treadmill a couple of years ago, when I had given up my gym membership. We bought it even before either of us really ran. But, I used it a lot when I didn't have the time to go outside and do a ride, walk or hike. I did a lot of hill walking on that thing.
I belong to a gym again and I would never go there for the treadmill! Only to warm up for a class. It's raining this morning; normally I would have gone outside for a run or ride at 5 AM, but instead, I ran on the treadmill. I'm glad I have it.