Mine has one on it, I will NEVER use it. I don't like the idea of spraying cold water on hot spindles. Water gets inside.
Seems like this was invented to sell more spindles. That's my .02 anyhow.
One of my customers has a nice JD mower and uses the washout every time he mows. When it comes in for annual maint the deck is clean with much less rust than the mowers that come in with lots of dried grass packed in it. Haven't replaced any spindles yet.