When physicists study efficiency, one of their most salient points is the importance of 'excess capacity'. It's important to plan non-productive time into your life.
Can you leave work early on a Friday, take a nap Tuesday afternoon, and still get it all done on time? If you leave that down time built into the system, you can handle the crunch time. Stomp the gas, swerve the bumps, and get through unscathed.
But if you work top speed all the time, you can't handle bumps in the road. And bumps happen. The IRS audit notice arrives, or a key team member gets hurt, a new product launches, your child gets hurt at school... Run your life on maximum efficiency and bumps in the road become major problems.
It's a terrible feeling when you stomp the gas and the engine sputters. You've got no burst of speed to get you through it.
Yes, it's more efficient to keep that pedal to the metal. Refuel as little as possible. Keep yourself barreling forward full speed, full time. It's also a good way to wind up broken down on the side of the road.
So leave some extra fuel in the tank and feel good about it. You know when to light it up and when to coast. With that extra fuel, you'll have what it takes to manage the bumps and stay in the race as long as you like.