If you save files often to a usb drive, that is write to a usb drive often, it shortens the life of the usb drive.
Backup is designed to minimize the amount of writing to a usb drive, for people running Tiny Core from a usb drive.
When you save, files are saved to RAM, not written to the usb drive.
When you turn off the computer, everything you changed is written to the usb drive. This is called backup.
When you restart the computer, the backup is restored.
I run Tiny Core from a hard drive, and don't use backup. Backup can increase the time taken to shut down and start up Tiny Core. Without backup it is very quick.
I use persistent home and opt. All changes are written to the hard drive when they are saved.