GoKawiilYour iPhone's cache is a collection of data stored to speed up operations instead of loading information fresh every time. For example, if a website has a huge banner image at the top, your browser may cache it. Then, next time you visit that page, it loads the banner from cache instead of wasting time downloading it again.
Cache usually doesn't use enough space to be concerning, and it helps apps run more efficiently because you aren't forcing them to reload repetitive elements all the time. However, you'll sometimes need to clear the cache to troubleshoot a problem or tidy up when these files are taking up too much space. While clearing cache isn't as straightforward on iOS as it is on Android, you can still remove those files when needed.
There's no need to do this all the time, however. Your iPhone will create new cache shortly after you clear it, so clearing cache constantly is counterproductive. If you're low on iPhone storage, even with the new base of 256GB, clearing your cache is a very short-term solution.