Short Answer: Yes

Long Answer: See Below

There was an ancient one attached to the old solar water heater on our roof - as the pipes running from its position, through the hole and eventually to the "distribution point" near the bathroom aren't secured that well nearest the water heater. 

I always thought it was some sort of "vintage pressure-relief valve," having an appearance not too separated from a steam-whistle. Our plumber decided to remove it when we got the new water heater, and I enquried as to what it actually was. "Water hammer arrestor" was the answer. 

Since it has been removed, anyone (particularly the kitchen/laundry) slamming taps makes a noticeable "THUNK," on hot or cold, whereas it did not before.

Even being a 30+ year old plumbing item, it still worked exceptionally whilst it was fitted.