I've never taken the oil off any of my blades. Hubby thought that the wheel needed to be lubricated or it could melt the cutter. While I do not cut in the speed of light, I have always left the oil on. I like the idea about the drop of machine oil on the cutter itself.
I find that I change my blade just like my sewing machine needle. After every big project or 2 smaller ones. This year, I want to experiment in table runners, so maybe after 4 of those, we shall see.