I do low-volume plans, prioritizing the Tuesday and Thursday high-intensity workouts, while adding 1 or 2 commutes (28 miles round trip) at a recovery/just-above-recovery pace. I frequently swap my Sunday workout on Trainer Road for a fast group ride or longer solo ramble because I just really need at least one ride a week where I’m not staring at a graph or already thinking about my work day. But if it rains, I’ll do the Sunday ride on Trainer Road as well.
The effect, overall, has been pretty close to the training stress of a mid-volume plan and it’s been working out great for me.
If you are new to Trainer Road, it’s worth knowing that TR’s brain trust generally recommend low volume plans, especially to start. There is a very small subset of riders who are best served by high volume.