Amnesia
Tails always starts from the same clean state and everything you do disappears automatically when you shut down Tails. Without Tails, almost everything you do can leave traces on the computer:
- Websites that you visited, even in private mode
- Files that you opened, even if you deleted them
- Passwords, even if you use a password manager
- All the devices and Wi-Fi networks that you used
On the contrary, Tails never writes anything to the hard disk and only runs from the memory of the computer. The memory is entirely deleted when you shutdown Tails, erasing all possible traces.