Noise, vibration, does nothing, no one knows, .... There's varying opinions on them. This gets asked a fair amount....
I'm of the opinion that the brake engineers had a reason to design these into the part. Just because no one is 100% sure what that reason is doesn't mean they're not needed either.
Right, I am here to find out the reason why.
Why would you even consider removing an item designed to keep the grease in and nasty items out?
Why only the top pin has it and not the bottom?
To reduce caliper rattling and slapping in floating caliper designs. There is no effect removing the bushings maybe lesser drag. My 02 Silverado had them in both lower and upper pins in the front calipers. When I used the wrong grease they swelled up so I removed them. Later caliper designs got rid of the bushing and opt for a tighter pin fit in the caliper bracket.
This is what had happened to my friend's ES330. His top pin bushing where seized. Removed the pin out and they were swollen. Then he removed it, no more seize and the braking force is better than before. So he was wondering if he can just drive without the rubber bushing on the pin.
It's usually on the leading pin, and slows the application so the trailing edge of the pad touches first, stopping squeal and evening pad wear.
Is that your final answer?