"Health clubs, glamorous girls, Nishikawaguchi" (health = a fuzoku format with hands-on service) — some people hear that and immediately know what's up, and some don't.
I'm 42 and still out in the field of this world, so I'll lay it out from a real-world point of view.
Why this topic matters
Information about fuzoku is surprisingly disorganized. Beginners especially tend to end up not even knowing where to start looking.
What this means in concrete terms
In a word: whether you know it or not changes the quality of the experience.
What I've written here is the distilled essence of 20 years of accumulated knowledge.
Last word
If you've got questions on this topic, drop a comment or hit me on social. And take a look at First Class Ruby while you're at it.