Understanding vendor functions

[chopsywa]

I am having difficulty understanding the purpose and use of Vendor functions. I notice the values are numeric for some brands E.G. Yealink and alphanumeric for others, like Fanvil. I can't see anywhere these values relate elsewhere in the system. I have looked at templates and there is nothing I can see there. I also looked through defaults|provisioning and nothing stands out.

I feel like this is a powerful feature, but I can't see how it is used.

Any clues?

Mark