I'll probably do more indoor trainer stuff this winter too. In the past I'd ride in temps down into the 20s. But this year our few really chilly days, just in the 30s, were enough to aggravate my sinuses so badly I'd end up with headaches and dizziness from clogged eustachian tubes. It was so bad this weekend I nearly fell over backward on an escalator Saturday night. Some friends and I were visiting an art gallery and going to dinner, and on an escalator ride we noticed it was an open sky courtyard and looked up -- and I nearly toppled over.
So I've avoided riding outdoors on days when my balance might be impaired. I'm taking a ton of stuff for sinus congestion, allergies and asthma but nothing really seems to fix it.
On the plus side, on my outdoor rides the past few weeks I'm faster than I was this time last year. So whatever I'm doing in training, inside and out, is working.
Mostly I use the trainer for two things: base miles at low effort, usually 2 hours or longer while watching movies or binge watching TV series; and short HIIT sessions, usually 30 minutes at most including warmup and cooldown. The long sessions are also useful for combining neck and shoulder physical therapy. I can pedal while doing upper body mobility exercises. Helps on longer outdoor rides, especially on rough pavement where my neck tends to ache after a couple of hours.
Several friends Zwift but I'm not that motivated by indoor training. I prefer meatspace brisk group rides to challenge my conditioning. That's hard enough. If I got dropped in Zwift I could just change the channel and watch something else. When I get dropped in real life it's just little old lonesome me watching the other folks get tiny in the distance. That's good motivation, especially when I have another 12 miles just to ride home.