Page caching is the single most effective performance optimization you can apply to a WordPress site. For most sites it is the single largest improvement available, and it costs nothing to switch on. Here is how it works, in plain language.
The Problem: Dynamic Page Generation
When someone visits a WordPress page, here is what normally happens: the web server receives the request, loads WordPress, runs PHP, queries the database (often dozens of times), builds the page from your theme templates, runs every active plugin, and finally sends the finished HTML to the browser. This process takes time — typically 500 milliseconds to 2 seconds on decent hosting, and much longer on cheap shared hosting.
And it happens for every single visit, even if the page has not changed since the last visitor — or the last hundred visitors.
The Solution: Serve Static HTML
Page caching changes the equation. The first time a page is visited, the caching plugin saves a copy of the finished HTML to disk. Every subsequent visitor gets that saved copy — no PHP execution, no database queries, no plugin overhead. The web server serves the static file directly, typically in under 2 milliseconds.
Think of it like this: without caching, your server is a short-order cook making every meal from scratch for every customer. With caching, the cook made the meal once, took a photo, and now hands out copies of the photo. The customer gets fed instantly, and the cook can handle thousands of customers without breaking a sweat.
What Gets Cached and What Does Not
A well-designed caching plugin does not cache everything. It automatically excludes pages that must stay dynamic: logged-in user sessions, eCommerce cart and checkout pages, the WordPress admin area, and any page that sets a session or authentication cookie. These exclusions are not optional — caching a checkout page would show one customer’s cart to another, which is a data breach.
Caching Out applies these safety exclusions automatically. When WooCommerce is detected, the cart, checkout, and my-account pages are excluded from caching by default. No configuration required, no risk of leaking customer data.
Cache Purging: Keeping Content Fresh
A cached page is a snapshot. When you update a post, the snapshot is out of date. This is where cache purging comes in: the plugin automatically deletes the relevant cached files when content changes. Publish a new post, and the blog index and any affected archive pages are purged. Update a product price, and the product page and shop archive are purged. The next visitor triggers a fresh cache generation with the updated content.
Further reading: A Beginner’s Guide to Browser Caching — the client-side counterpart to page caching that prevents repeat visitors from downloading the same assets twice.