What does reset all settings do on an iphone

A factory data reset erases your data from the phone. While data stored in your Google Account can be restored, all apps and their data will be uninstalled. To be ready to restore your data, make sure that it's in your Google Account.

Most commonly, people reset their iPhone because they are experiencing major software errors, like issues connecting to networks or apps crashing. Resetting the phone to its factory settings should resolve these errors and restore normal functioning. It's also smart to reset your iPhone before selling it.

When you Erase All Content and Settings, it completely resets your device. All information including apps, photos, videos, contacts, messages, calendar, or music etc. are lost. In order to restore your iPhone after factory reset, first take the backup of data in iCloud or iTunes.

Restoring your Apple® iPhone® to default settings helps when the device crashes and resets itself or when apps freeze / hang or reset the device. All customized settings are restored to default values (personal data isn't affected) including: All Sound settings (e.g., ringtones, notifications, etc.)