When your browse something your web browser, a cache of the websites you visit is saved by the browser in order to load the subsequent visits quickly. Similarly, Linux too keeps a system cache – apt-cache, application cache, etc. – so subsequent loading of the application will be very fast.
Cache is a good concept when viewed from a user’s point but do you know it keeps utilizing your system’s memory. Also, at some point, you need to ensure that all the unnecessary data or junk files are deleted which are usually in the form of the cache so that your system remains fresh and less loaded.