The big difference in synthetic vs. dino is that synthetic can take much higher tempertures. This is important for certain motors. If your motor doesn't need high temperture oil, then there really is no reason to use synthetic. Dino oil doesn't wear out. It gets contaminated and diluted, just like synthetic does. That is why oil needs to be changed, no matter which type you use.
I tried sythetic once That motor had numerous oil leaks. Could have been a coincidence... But synthetic does pour like water, so it makes sense that it could get by seals easier. Which brings up cold weather performance. In VERY cold temps, it should do better.But I don't think it gets cold enough in the lower 48 to matter.