I will give you a simple example of the browser cache. This website has enabled the browser cache option for 30 days. What does this do? If you turn off your internet and reload this page, you can view this page (without the internet).
But the styling code is not cached. So you will see this page without any style.
What are its pros and cons?
This page will load faster during the 2nd repeated visit. But it will also increase your device memory. (But here the cache automatically gets cleared in 30 days).
The CPU processor itself has dedicated memory storage. This stores (copies) some data which requires frequently. This eliminates the small fraction of time which requires the CPU to collect the data from RAM or hard drive.