There may be a number of reasons to hard reset iPhone 8.
Usually, people do this to fix any problems the iPhone 8 may be showing and make a fresh start, just as it came out of the box.
Another reason is when they are about to sell their iPhone, so that their private data and apps are deleted quickly.
What Does a Hard Reset Do to Your iPhone 8 (Plus)?
A hard/force reset will revert your iPhone 8 to its factory settings and delete all the data stored on it. In a nutshell
all your third-party apps, user data, and settings will be erased and restored to factory version and your iPhone 8 will act like it’s brand new.
The easiest way to reset your iPhone is the inverse of turning it on.
This method is often referred to as a “soft reset,” meaning you won’t lose any data and nothing will be deleted from your phone.
The best time to perform a soft reset is when your phone is running a bit slower than usual, an app isn’t opening or working properly, or some other relatively small problem has occurred, but your iPhone is still responsive.
Step 1: Press and hold the Sleep/Wake button until the Slide to Power Off slider appears.
On the iPhone 6 and later models, you’ll find the Sleep/Wake button on the right side of the phone.
On the iPhone 5S, and earlier models, the Sleep/Wake button is found on the top.
Step 2: Rest your finger on the slider, then swipe to the right.
Step 3: Once there is nothing on the screen and it goes black, press and hold the Sleep/Wake button again until the Apple logo appears.
Alternatively, provided you have iOS 11 or later installed, you can go to General > Settings and scroll to
the bottom where you’ll find Shut Down. When you tap Shut Down, you will see the Slide to Power Off slider.