Yeah, so an entry process is just "what it takes to start loading your page."
There is still an entry process, even with cached files. For example, a visitor could load a page on your website... The entry process involves showing the correct file(s) and information, however some of that may be cached and some may not. Caching is good all around, and it definitely improves site loading speeds.
For example, imagine you have an image that is 10 MB in size. This image needs to be "downloaded" by the user, so they can see it. This causes 10MB of bandwidth to be used on your server, and it also involves some basic processing because your server needs to fetch that file and display it. However, if the 10MB photo is cached then your server is only really saying "hey display this file" and the cache is saying "cool, we already cached/downloaded that file", so even though the 10MB photo is displayed again, it's in the user's cache so it doesn't need to be re-downloaded to display. This means that the cached image only uses the 10MB of bandwidth for the first load (per user), and doesn't use any bandwidth to display the second time. Of course, other elements and parts of the page may be re-downloaded and use some bandwidth. However, the more data you have cached, the less things need to be re-downloaded, and the faster your site becomes.
Caching is great, but be careful that you don't cache "too much". For example, if you have a page that changes every single hour (for whatever reason), and it's cached, then users won't see the new versions. For example, you could create a script that makes your logo a different color every 10 minutes. Perhaps the file is called "logo.png" and your script REPLACES logo.png with a new version every 10 minutes. Well, even though the file has changed completely, the cache doesn't understand this. This is because the cache knows that "logo.png" is already saved in the cache, but it doesn't know when a new logo.png is there unless you give it specific instructions telling it that the file has changed.
On the flip side, not caching anything (using a forced no-cache) is bad because it forces every user to re-download every asset on your site each page load. This is not good, even for things other than images and videos. For example, large JS / CSS or other files can be cached without much issue, so there's no need to force a no-cache on those files unless they (for whatever reason) change frequently or dynamically.
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