Connection scanning in explicit match commands pre-dates the barrier mechanism.
It essentially lets adventuron know when a direction will lead somewhere not covered by the connection map (like directions in a maze for example), or context specific enter and exits, or directions.
I think I'm going to change adventuron to use basic exit list calculations by default. The barrier mechanism is far more reliable at blocking and enabling conditional exits, but the mechanism can still be switched on for games with mazes (where connections mappings are dynamic and made via the on_command {} block.