All the feedback you've gotten here has been great. I do coach cyclists, runners and triathletes. Rest weeks and rest days are really important. They allow recovery and help to prevent burnout as ny biker mentioned.

I usually schedule a rest week after 3 weeks of harder training and at least one day per week for athletes under 40 years old. Older than that, they get a rest week after 2 weeks hard training and 2 full rest days per week. Obviously these are only guidelines and depend a lot on your athlete but it is generally true that as we get older we need a little more rest to recover from hard workouts and since endurance is usually pretty good (depending on your background) I will usually sub a rest day for a lighter effort endurance day.