This knowledge has been forgotten over the years. In the olden days people always stood a milk jug under the steam wand. This was not because they would leak, although sometimes they did…but for another reason. These “compression close” knobs as I call them are very, very good if you use them right, most people don’t and instead of ending up lasting 10-15 years they last 3 years. Much longer than the “no compression” type.
When you close the wand, do it very, very lightly…1 finger will do, until it “just” stops. Shortly after, the water/steam will start to drip out again. This is because things have contracted slightly as it cools, and the valve becomes slightly open. You are then meant to close the valve a little more, very, very lightly, until it just stops….it won’t start leaking again. Do it this way and that Teflon pad seal will last 10-15 years.
Instead, people think ah I didn’t close it enough and next time close it harder the first time, it might still leak and the cycle repeats, the seat deforms and you need a new valve…or the cup holding the seal splits. The same logic applies to hot water taps as well.