Whenever you visit a website on an iPhone or iPad, snippets of data are saved to your device. Cookies and other cached data eventually start to take up significant space, so you may want to clean them out. Here’s how.
Periodically clearing the data that iOS stores can be a good idea for a number of reasons. Beyond the fact that collectively these websites store quite a bit of data on your devices, that data can be used to track your visits, too. Websites save cookies to your devices to be able to tell when you visit again, and even though that can be beneficial to keep you logged in and save preferences, not everyone likes it.
If you want to make sure that websites can’t keep tabs on you, you might also want to make sure you delete the information they save to your device. If you’re short on space, you might just want to clear out of all cruft, too.
How to See and then Remove Data
To get started, open the Settings app. Next, tap “Safari.”
Now, scroll to the very bottom of the screen and tap “Advanced.”
Next, tap “Website Data” at the top of the screen.
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Source : How to See and Remove All The Data Websites Have Saved on Your iPhone or iPad