My wife and I have never done this in our home, but quite a few people
ask visitors to remove their shoes before entering their home. In a way this makes sense.
When you walk around, you step on every kind of filthy things and smear them over the
floors when you enter the house.
On the other hand, bacteria, viruses, germs, need nutrients to survive. Rugs, flooring,
shoes... are not especially conducive to their growth.
Same thing with tennis balls. Yes, they will pick up icky stuff from the courts, but for the most
part we have already developed defenses, to these things.
Recall, the movie or book- War of the Worlds, the alien invaders had not developed
immunities to Earth's diseases. They died, the Earthlings (immune) lived. It's as
simple as that.