Tor Browser protects your traffic. It does not protect the machine underneath, which is still your everyday system. Tails closes that gap.
What Tails is
A complete operating system that boots from a USB stick, routes everything through Tor, and forgets everything at shutdown. Nothing is written to the machine's own disk.
What it protects
A device examined later carries no record of the session, and no application can accidentally reach the network outside Tor. Those are the failure modes Tor Browser alone leaves open.
When it is worth it
For casual use, Tor Browser on your normal system is fine. For anything where the machine remembering the session is a risk you care about, Tails is the tool. Boot, use, shut down. The board recommends it for readers whose threat model includes their own hardware.