I didn't see one in my car (71) that I just recently restored.
Wondering what car years these came on?

The yellow arrow points to the small sheet metal cover that goes over the parking brake cables inside the cabin between the rear of the handle and where they exit to the rear of the car.

And how necessary are they? Suppose they keep some trash out of the area at the most.

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no,
sorry for my terse reply.
Early cars had the equalizer yoke covered by a formed corner of the carpet and as Mark said no spring to
help release the cables

Not the early cars. They didn’t have a spring assist to the firewall for the short e-brake cable.