On the downside, oil does not last as long as grease, so your bearings will require more frequent lubrication. Note that oil and grease both share the components of base oil and additives. The difference between an oil and grease is that grease has a thickener. The thickener makes grease easier to retain in the bearing, provides a better barrier to contaminants, and adheres better to the bearing surfaces. Since grease is thicker than oil, it also has greater resistance, which means slower bearing spin.
Synthetic lubricants are man-made.
They are blended from various chemicals and have molecules that are uniform in weight and shape. The uniform length of synthetic lubricant polymers allows them to slide more easily over one another. The result is reduced friction and a faster spinning bearing. Synthetic lubricants run smoother and longer at all temperatures, whereas petroleum-based lubricants form deposits at high temperatures and solidify at low temperatures. Greater film strength protects bearing parts better.