A public article and a customer account are different cases
The text of an article or a service page is usually the same for every guest. An account, a cart and the results of personal actions can differ. You can't blindly serve them from a shared copy.
Even a public page can contain dynamic form data. You either need to refresh it separately and correctly, or pick a different caching method. A fast page with a broken lead form is not a successful optimization.
Plan when a cached copy goes stale
Editing text, prices, menus or a post's publication status should refresh the affected pages. On a blog, it's not just the new article that matters, but also the article list and recommendations. Make sure a scheduled post doesn't show up early.
Cache can live on several levels: the application, the server, a CDN or proxy, and the browser. This also affects your choice of hosting. Without a map of these levels, it's hard to explain why some visitors see your changes and others still see the old version.
Test speed and correctness together
First find out why your website is slow. Compare the first and repeat visit, a guest and a logged-in user, a page before and after editing. Test forms and simultaneous requests. Exceptions should be explicit, not depend on some random cookie.
Technical support that includes speed optimization should rely on these checks. If caching needs its own server configuration, discuss server solutions with data freshness in mind, not just the top score in a single test.
