AC is air cleaner, and that line goes to purge control solenoid on the dside firewall, then from there to TB. ECU turns on the solenoid when it's time to vent the canister. Carb line is blocked off (that one goes to the fuel bowl on a carb - not needed with fi). The tank line comes thru a noodle bowl of lines, an overfill valve, a two way valve, some seperator tanks (condense out some fuel vapor and drain the liquid fuel back to the tank) and a mess of hoses.

If the AC line is vented to atmo, so are the fuel fumes, instead of being burned up in the engine. It wastes some gas to run unhooked. And pollutes the air, adds to ozone...