In CrossFit it is magical what happens when we get to rest for a day. You actually get stronger, can run faster and jump higher. Hard to explain why without a medical license… Going all out for weeks, on the other hand, almost always hurts performance.
At work I believe the same is true. Taking time off and unplugging for a day (I do mean Blackberry/iPhone off, email untouched) can help recharge not only batteries but enables us to solve tougher problems, reenergize projects and relationships. When the task gets too tough to tackle, maybe you need to walk away from it and come back a day later. Works like magic.