To me the best reason to use synthetics is to extend the drain interval. I am commuting 750 miles a week and just got fed up with changing oil all the time, so I switched to synthetic (Walmart housebrand synthetic) and 10,000 mile intervals. Walmart also has Rotella 5W40 synthetic and I am going to switch to that next time. I might even increase the interval again. I seem to remember when Mobil ! first came out they said one could go 25,000 miles between changes. Well, that didn't last long because someone quickly figured out they were going to be selling a lot less oil if everybody started doing that. I will admit there is a psychological benefit to changing oil and the more often you do it the more "feel good" there is.