I think there is a lot of grey between being 100% compliant with a training plan and having no training plan at all.
The interesting thing I have learned from this discussion is that the miles that may interfere the most with optimal training are miles that are not sufficiently challenging to produce a training benefit but are sufficiently challenging to interfere with recovery from a hard ride.
I like to ride hill repeats. But I think I should skip those on most rides and have designated hill repeat training days.