Here is the VIN decoding for Unabombers VIN number. I know it says LOG, but that's just for quick reference in case someone needs to go back and forth between multiple cars. It gets erased when the program is closed. Trust me on this one. The parts catalog isn't linked to anything else.
Here is (just as an example) the correct clutch disc for his car with VIN filtering.
The same listing without filtering.
Hopefuly this gives you an idea of why many would want to know the VIN. It's faster and more reliable than just knowing the production date. In most cases finding something without the VIN isn't a problem, but in some cases it makes a world of difference.
Yeah, so... maybe this helps. Maybe not.