A friend gave me an old underused Cycleops trainer last summer while I was recovering from injuries. Best thing for staying in shape. I can hardly ever sit still and do just one thing, like watching TV or movies. So I combined bike trainer sessions and binge watching sci-fi shows I'd been wanting to watch anyway. By the time I was able to get out for road rides again I was still about 85% of my pre-injury fitness.
It's also great for regaining confidence. A friend suffered a debilitating arm injury last year when a free-range dog knocked her off her bike. But as much as the physical injury, she seemed to have lost confidence. She got an indoor trainer, then Zwift, joined a group suited to her abilities and after several months had regained her confidence and joy in cycling again. She's back on the road doing group rides with friends.