Caching stores temporary copies of your website to help it load faster and reduce server load.
During any kind of development work, you’ll want to have all caching turned off so that you are always seeing the most recent changes. Once your website is approved and ready to go live, you can activate your caching to improve speed and performance.
WinningWP sums this up nicely:
If I ask you what the result of 5 x 3 is, you’ll know the answer is 15. You didn’t need to calculate it, you’ve done this multiplication so many times in your life that you no longer need to — you simply remember the result without having to do any mental processing. Well, that’s kind of how caching works.What is Website Caching and Why is it so Important? – WinningWP
Websites are generally viewed hundreds, thousands, or sometimes even millions of times per month. Normally, each time a browser requests a web page, the server has to do a bunch of complex (and time consuming) calculations. It retrieves the latest posts, generates the header and footer, finds your site’s sidebar widgets, and so on. However, in many cases, the result of all these calculations will be exactly the same. Wouldn’t it be great, then, if we could simply make the server remember the final result, instead of processing each request separately? This’s exactly what caching does!
How do I add caching to my website?
One of the more popular ways to add caching to your WordPress website is through a caching plugin.
Unfortunately, answering the question “which one should I use?” gets to be a little complex. Each caching solution, and caching in general, comes with some trade-offs. Some caching plugins might work better with your stack than others, or you just might feel more comfortable with one over the other.
Your best bet is to try a few, test their performance, and ensure that they are not affecting your website in an adverse way.
The other thing you need to consider is your hosting environment. Some hosts, like Kinsta, provide all the caching you need at a sever-level so there is no need for a plugin. Cloudways, for instance, provides both a plugin and server-side caching.
Never forget your cache!
Caching is notorious for causing issues.
Not seeing the latest update you made? Probably because of caching!
Something stopped working that was fine a minute ago? Check your cache!
Seeing different versions of your website from different machines? Yep, that’d be the cache!
When you implement a caching solution, you’ll need to be aware of it at all times and make sure to manually flush it any time you make changes to your website. It can take a little getting used to, but the benefits in speed and performance are generally worth the headache— especially once you find a caching solution you’re comfortable with.
Do I have to use caching?
No, you aren’t forced to use caching, and in some cases (on very small, lightweight websites) I’ve actually seen better results without it. It’s a good idea to test your website’s loading time and performance both with and without caching. You can use speed tests like GTMetrix or Pingdom to test your loading time and run several tests with and without caching to make a determination.
Speed tests aren’t everything though. Take the time to view the website manually and see how fast it feels as you use it. If caching isn’t giving you a noticeable boost in performance, it may not be worth the trade off.