This mode exists to enable the Tor browser's idea of fingerprinting resistance. The reasoning for why it works the way it does is documented in their design doc

This mode exists to enable the Tor browser's idea of fingerprinting resistance. The reasoning for why it works the way it does is documented in their design document at https://2019.www.torproject.org/projects/torbrowser/design/#fingerprinting-linkability https://2019.www.torproject.org/projects/torbrowser/design/#....