I try to go at a pace that is brisk but comfortable, definitely not all out, my commute is about 10 miles with hills. To go all out would have me arrive at work in a sweaty mess and fatigued, not a good start to the day, for the sake of saving five minutes, not worth it. In addition, if I were to go all out starting on Monday, by Wednesday I would be so weak and groggy that I would have to drive to work, again, what is the point, virtually no gain, with significant disadvantages (the assertion of keep at it and you'll get fitter doesn't work for me)?