One of the big things that Plan Builder doesn’t do is 2-a-day… which is a pain for combining commuting and training because you’ve got to get home! (couple of comments about this below *)
I only train outdoors. Partly because I don’t have a decent trainer, partly because I live in a place with a great climate (sorry), and I have a 21km commute on mostly good paths and quiet roads (sorry). What works for me is intervals in the morning then Zone 2 on the way home.
I knowingly accept that the morning intervals are compromised by traffic, junctions, roadworks, but also hope that I win a bit of outdoor riding specificity. But on the odd occasion that I train indoors I’m always a bit taken aback at the physical difference.
If you don’t have a good outdoor route for the longer or more intense sessions, then why go 100% outdoor? If you plan to do a few key sessions on the trainer then you’ll have more effective training and commuting can be bonus Z2. It feels a bit daft doing an indoor trainer ride then getting in the car, but it does mean you can really do quality training.
(* So what I’m doing is letting PlanBuilder give me 2 bike workouts a week (Masters Olympic Tri plan). I’ve put these on Monday and Weds, they’re usually 1hr which matches my commute. I change each one to outdoor and set the workout time to 8h. Then I add a 1h15 Endurance or Recovery ride for 18h. I do this in advance - I’ve stopped using TrainNow for this as the suggestions are always the same, I don’t think it really takes into account the morning workout and I always just want to have a visible power limit on the Garmin so I really do stick to Z2 on the way home. I’ll choose Recovery to have something easier on days with a VO2 or threshold workout in the morning. If I’m feeling up to it I’ll add Endurance rides for extra commuting on Friday
If I don’t set workout times then my Garmin will keep proposing the morning workout and I end up having to delete it.)