Do you carry a knife that has a bearing pivot? Bearing-pivot designs have led to a renaissance in knife manufacturing over just the last 5-10 years leading to a 2020's market absolutely stuffed with high quality, reasonably-priced pocketknives sporting ball bearing pivots and very snappy, authoritative actions.
Thrust bearing mechanisms dramatically decrease friction between knife blade and handle, allowing knives to open with less effort and more speed, with the added advantage of easier-to-tune pivot screws for easy deployment.
If these knives have a disadvantage when compared to knives running on phosphor bronze or polymer washers, it's that they tend to be more open to allowing abrasive dirt into the pivot area due to poorer sealing. Contaminants like dust and sand are able to enter the pivot area by their moving into the spaces between each ball in a caged assembly or IKBS raceway.
Abrasive Wear in Metal
Once a hard particle of sand, dirt or grit enters between two moving parts of a pocketknife it will tend to grind against them, leading to scratching, pitting, and wear. This damage eventually leads to eroded bearing surfaces that are no longer smooth and accelerating wear to balls and races during ordinary use. In the worst case, steel or abrasive particles can actually embed themselves in bearing surfaces, turning a ball bearing into a mini sanding machine!
Worn surface of ball bearing
Debris embedded in surface of steel bearing
As we discuss in the above video, a small amount of wear to knife races and balls can actually lead to improved action and blade-feel, and this happens during ordinary usage, but we absolutely want to avoid uncontrolled wear, scratching and other damage.
Knife Oil not only makes your knife operate more smoothly, it also protects metal parts from taking damage during everyday use! It achieves this by cushioning parts in a slippery fluid, and even more importantly by suspending contaminants. With particles in suspension, they tend to flow out of the way of contacting surfaces due to hydrodynamic forces on the suspended particles that travel in currents within the lubricant.
The TLDR is that a high quality knife oil not only makes your knife feel super-smooth, it also protects and cleans your knife as you use it.