I can't at all explain why this happened, but my 11 Lexus GS350 warped front rotors and all I ever do is keep the car in gear and use the engine to slow down. There is even a Standard Simulation mode that allows me to downshift. I've used this method to nearly completely stop the car while driving around town. I only hit the brakes if there is a car directly behind me that needs to see brake lights to avoid slamming into me. Even then, I use downshift method to slow down. Not sure how this works as it is an Automatic, but seems downshifting does in fact allow the engine to mimic a manual transmission. It is a pretty cool feature that most cars seem to have these days. I use my A/C almost exclusively, so I'm doubting fuel efficiency is at all increased when doing this slow-down method. 
Most modern cars can idle for over an hour on a gallon of gas, so saving a sip of fuel just doesn't amount to much. Saving fuel on a freeway is the true question to ask. Another one is how in h3ll did my rotors warp?!