At the end of each training block I take one week to drop the intensity and volume slightly to shed long-term fatigue. These are my rest weeks. I still workout every day, five or six days a week, so they may not look particularly restful. But compared with what I did in the previous weeks they are definitely a respite.
One advantage I've found is that they are a rest for my mind as well as my body. Endurance sports require a lot of intense concentration, whether it is pushing yourself beyond your normal limits or trying to hit a specific intensity during a key workout. This is necessary to achieving your best, but can take some of the fun out of sports.
One thing I've started to do on rest weeks is to allow myself to do less structured workouts. Rather than doing a swim session with repeat 200 yards at Zone 4 with one minute rests in between, I'll just do fast 50 yd swims until I'm tired. No looking at the watch, no counting mileage or checking heart rates. Just fun exercise.
On Friday night I went for a light two mile run, and on my way back to the apartment I was feeling great and really wanted to pick up the pace. At first I rebuffed the temptation, because I wasn't planning on doing any speed work until I was running longer distances. But my legs were calling out and I couldn't think of a good reason against it.
My stride lengthened and my Minimus MT10's started to feel like my old racing flats. As my breathing increased I gradually accelerated into an all out sprint and the pavement and the trees whipped past me. I hadn't ran this fast in more than a year, and it felt spectacular. This is why I run, not for the PR's or the medals or the crowds but for the pure rush of going fast.