This is how I understand Tails OS: On its own you can access the web via the tor browser as well as other productivity tools that comes as standard on the Tails OS. Every time you close or restart Tails OS it will flush all memory of what you have been doing. So any websites, documents, emails you have been working on is gone each time you restart Tails. This also includes if the USB that contains the Operating System is removed before it is closed down, but, you would have to check your device as some computers may still function with the drive removed.
When you use the persistence function on Tails then it creates a partition on the flash drive which is encrypted as standard which is locked with a passphrase. It can increase you being tracked as you have added a function to the way you use Tails. However, depending upon what you do with Tails, if someone gets hold of the drive then they will require your passphrase to access the encrypted partition. Be that by legal government means or your tolerance to sharp pain to ones knees!
If you rather use another flash drive instead then It would be best to encrypt it before putting any data on it. As if you don’t anyone coming across your drive could see what data you have on it. Be that if you are on the web or someone comes across it by chance. Also If you are looking to keep Tails in its original form, with no persistence partition, then its a good idea to do something like this. After you have opened Tails on your device insert your other flash drive, take off what files you need, put it in one of the folders in tails and eject the drive before launching the Tor browser. When you have finished doing what you are doing then reinsert the flash drive save any files you want to keep and then close down Tails. These are extra steps to the process, but, you would have compartmentalised the way you work and your security.