What you are looking at is the bottom of a connecting rod. The crankshaft goes through the big hole you are seeing, and the piston connects to the top hole that is just out of sight.

The thin piece of metal in front is a bearing. This is all that keeps the crank from rubbing against the rod. After the motor has run for a few thousand miles something is going to wear out, it's better if it is the bearing than the rod. You see, the cap of the rod can be removed and the bearing can be replaced.

The reason I think it's important that you see the bearing is because it's important that you understand that the bearing is only a piece of metal that wears out instead of the very expensive crank or rod 

The IMPORTANT fact is that it still costs a lot of money to replace the bearings!!!

So oil changes are Critical!!!

Oil is pushed into the bearing through the hole you can see in the bearing.This leaves a barrier of oil to help stop wear.

So, the cleaner the oil, the longer you can go with out replacing the bearings

My customers who change their oil every 3000 miles will consistently go many many more miles without engine repair. Other advantages are better gas mileage and increased performance.

Its important to note that oil additives are not as important as CHANGING THE OIL.