Well, you get the drift right? There’s a ton of data on your iPhone that is mostly not needed but is still using up a lot of space on your iPhone. Things really pile up a lot on the iPhone just like on the computer: browsing cache, app cache, unwanted files, cookies that may be potentially dangerous. If not given the due attention, the smartphone can get cluttered for space thereby losing the famed speed.
Just like any other human-made device, iPhone also needs the care to run smoothly and deliver the desired performance.