This is an ideal device for quickly brushing the grounds off of your tamper between tamps. When you tamp a shot, it's inevitable that small coffee particles (grounds) will cling to the bottom and sides of your tamper, both because of ambient humidity and static electricity.
It's not a good idea to do a new tamp without removing these grounds, since these grounds will usually wind up on the group rim. Inserting the group with small grounds on the rim will wear your group gasket out very quickly.
For the home barista, where you aren't making lots of shots, and where speed is not a problem, you can simply brush these grounds off with a towel (or even with your hand). In a coffee shop, you can't do this. Not only is it NOT entirely sanitary, but it takes too long. Instead, simply insert the tamper base into this cleaner brush, and give it a half twist. This will remove the grounds.
This is an essential tool when you are doing volume espresso!