it actually depends on where you live, time available, training objectives, etc.
But I cant see what is the benefits of riding the trainer at such low intensity. Burning fat is not a valid point, if someone wnats to lean down, the answer is simply burn more calories. Burning calories is done via workload, you're better off riding tempo intensity, that way more calories are burnt.
I guess most people riding the trainer are time constraint people, hence why I dont find any argument in favor of L2 riding. There are specific adaptations (heart contraction, efficiency) to riding this intensity but like I said, I would not bother with these during winter time.
Again, winter is relative. Winter here means its dark at 3h45pm, road full of snow/ice/salt and impossible to ride safely outside.
Given the OP sound quite new and wants to loose weight/build a base, I'd recommend lots of L3-L4 intensity work. Building base with L2 is an old school outdated principle, especially for amateurs who dont have 20-30h available to train each week.
I think the better question is: "how do you avoid riding the trainer?". When sunrise and sunset times coincide with workday start and end times and riding after dark is near suicide given traffic and road conditions it becomes a bit of a necessary evil, but I'm always looking for ways to avoid it. Not to mention the contradiction of winter being the point in the season that we're supposed to be putting in longer, easier rides at the same time that there's no practical time to ride.
I think the gloom of the impending winter is hitting me hard this year...
I do intervals on the trainer once a week, 20-30 min warm up, 45 sec sprint seperated by 2 min x3, then 5 min break, and repeat 2 more times. That is the only real workout i do on my trainer, 3 other times a week i will ride some miles on it after playing 1-3 hours of volleyball, but that is mostly high resistance low cadence to get a little extra in my work out. It is hard for me to get enthused about a trainer when i only use my road bike to go back and forth from the bar.
I generally dedicate 2 workouts/week to interval training. These are short, high intensity workouts with TSS bellow 100 (including warmup and cool down). The other 2 workouts are endurance based and I aim for 2+ hours for those workouts. Total weekly workouts are about 8 hours.
For me now is FTP improvement time. I will do a few blocks of true base building in Jan/Feb where I am going to shoot for 12-14 hours.
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