You then took that clicker to your local arcade, and clicked one of the corners of the CRT, that would send a shock through the system and add credits to your game. I believe this was because the CRT was grounded on the same ground lines that the mechanism for physically checking a coin had gone through the system.
Suffice to say, they caught onto this over time, and added some form of an alarm into it. But up until then... Those were truly the best times.
Those systems are occasionally used in bars in the US, though they've dropped the whole plate and it's usually just arms where the holes are.
To my understanding, at least in the US, they aren't used for deep-cleaning anything. That happens with soap and water in the back still. The upside-down-showers are used to clean out the dregs of someone's glass when they get a refill (you give them a glass, they give it a quick rinse, refill it and hand it back), and as a quick rinse for new glasses to clean up water stains/detergent residue and anything that might have fallen in since they were cleaned (hair, dust, etc).