Rubber feet (?) on backboxes - why?

[Durzel]

I'm probably being really simple here...

My backboxes have rubber feet on the bottom of them. As far as I can see there is never any time that they would make contact with anything?

When tombstoned with the backbox strapped it's higher than the bottom of the main cabinet. When the backbox is upright they clear both sides?

What's the craic?

 

[replicas]

They are not rubber they are nylon gliders , installed at factory to protect back box while waiting to be installed to cabinet.
That's it.

 

[Durzel]

Cheers