Performance benchmarks use scores from Pingdom.com, WebPagetest.org, or GTMetrix.com.

Oddly, no one mentions speed test scores don’t matter. It’s milliseconds that count! Or that Google PageSpeed Insights is a test designed to create site-owner anxiety. Boasting about a PageSpeed Insight 100 test score is ridiculous. We’ve seen 12-second pages get a 100 rating with this test. A joke. Many blog authors claim they find speed salvation using popular WordPress caching plugins.

On an optimized site, caching plugins make little difference in load time. The initial visit is the critical one for the first impression. Only 5 percent of PagePipe traffic is repeat visitors (500 visitors per month). That’s very low. But not uncommon.

We’ve inspected big sites (1 million+ visitors monthly) with high return-visitor rate (80 percent). The high return rate is often from sending frequent subscriber push notifications. These are swirling aggregated news sites. The recent content is brand-spanking new. There’s little benefit from caching.

Author’s Jonathan Sulo (Servebolt) and Tom Usbourne (GeneratePress) and our staff (PagePipe), agree. Caching plugins often break your site and cause problems more than help. It’s usually file concatenation reducing requests that are the biggest problem.

We install two plugins: Cache Enabler and Better WordPress Minify. That separates the function of minification. We then selectively deactivate an offending plugin on pages. Or disable it completely site-wide without sacrificing the benefit of the other plugin. Those are discrete plugins with few settings or none. They work. A do-everything caching plugin is dangerous in the hands of novices. Not to mention the site drag caused by the heaviest caching plugin like WP Super Cache (2+ million active installations) and W3 Total Cache (1+ million active installations).

Cache plugins speed up the requests that are cached, but slow down the requests that are not cached. Since a regular cache hit rate is somewhere between 10 and 25% a cache plugin will slow down the site for 75 – 90% of your visitors. – source

On an extreme optimized site, there may be a few 100 kilobytes of page weight and only a dozen requests. With no popular plugins, that site will load in under 1 second almost to anywhere in the world. No CDN necessary. No caching plugin. No minification plugin.

Do we ever add plugins to improve scores? Yes. This is for the site owner’s psychological benefit when they examine test results. These include discrete plugins like:

• lazy loading
• minification
• far future expiration
• remove query strings from static resources

These lightweight plugins make scores look good. But their actual contribution to mobile speed is small. They don’t slow down a site, so why not make test results appear the best possible?

If your site is fast, adding caching satisfies fanatic obsessive-compulsive speed behavior. From which we suffer. We admit it.

Where is “caching” truth? There is none. All blog reviews of caching plugins are self-serving and biased. Especially benchmarks selling affiliate Hummingbird or WP Rocket plugins. Are we surprised by the cherry-picked results? Nope.

WordPress Plugins like W3 Total Cache work like all other page caching. They store a version of a pre-generated page to the file system or memory, and serve it to users until it expires. W3 Total Cache is being used by 1 million websites, but that doesn’t mean it is a good idea. Especially not if you use fast hosting.

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W3 Total Cache is a very large plugin, and for most sites – this just adds a whole lot of unnecessary code to the website. More code, means more things can go wrong. …

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W3 Total Cache talks about getting pages to load in less than 2 seconds showing off a theme like Twenty-sixteen. To make it clear; a similar test [on fast hosting] will be delivered in about 100 milliseconds without the use of caching, not seconds. –source

WP Rocket is a paid plugin ($49) advertised as a caching plugin. It’s a multi-function plugin doing much more than caching. WP Rocket claims they create pre-cached pages. This happens on plugin installation, and every time a page changes. Does this make a speed difference?

WP Rocket works or helps most sites. We’re sure they do what they say. But there are no documented benchmarks of performance improvement from their special pre-caching feature. This feature is a marketing tactic to improve product differentiation. It’s brilliant marketing. We remove WP Rocket and use free plugins to achieve the same or better results. All we have is experience of repairing client sites. And reducing their annual site overhead costs.

DISCLAIMER: We use caching and minification on PagePipe blog – but not on our store. Caching is not recommended with eCommerce plugins like Easy Digital Downloads and WooCommerce. Checkout-page breakage results.