A while back, I was injured and had to use a walker for a few weeks. I
bought a used one at a second hand store. It came with tennis balls on
the legs. I was just putting it away and noticed there are rubber "cups"
on the legs beneath the tennis balls. This makes me wonder why they put
the cut-open tennis balls on the legs. And I see this on almost every
walker used by people.....

Do the tennis balls provide a better grip than the rubber, or is there
another reason?