Enable caching for all visitors — Does nothing?

So I have a website where I’m using the WP login system to make user accounts that lets people log in and do some custom tasks (but nothing else) — Basically Subscriber level accounts, but a custom level. They aren’t shown the WP header, they can’t access wp-admin, etc.

I refactored the parts of my pages that care about their logged-in status, to all be in javascript/ajax requests.

The goal is to then turn on the “Caching for all visitors” option. And they would be given cached pages, and ajax requests would be made for the small-bits that care about them being logged in.

However: It appears to do nothing?

When I have that feature on. And am a logged in user … it regenerates the page every single pageload. Zero caching.

The only way I can force caching to happen is to turn on the ‘make users anonymous’, but then that, of course, breaks my ajax requests since the users are ‘made anonymous’ for those requests as well!

So what is the “all visitors” option really supposed to be doing then? Since it’s not doing what I’d have expected.