If you find that an app is not functioning the way it is supposed to, clearing the cached data might solve this problem. In addition to that, if you want to free up some space on your storage, then too, clearing cache is a good practice. Still, it must be kept in mind that cached data only occupies a small part of your storage. So if you want to clear a large part of your storage, you will want to delete some applications that you no longer use. Other than that, you can transfer some files to an external storage device such as an SD card or a USB.