When enabling Session authentication across servers, the token issued by a server can still be used even after the session has been completely ended on the server and on the browser. If a user issues a request to the server using the same token, you will notice that the token is still active. The token only gets completely destroyed upon reaching the token expiration time. This can be a cause of concern if an attacker gets information about the token.
The idea on having an option to select whether LTPAToken should be completely removed/or usable when sessions end can be a good added line of defense from attackers.