As in someone sat at the glass doors between A6 (the last domestic gate) and A7 (the first international gate). If you are arriving from a domestic flight and going to say T234 so heading for the airside bus you need to go from the domestic arrivals area past that person in to the connections area, and then down to the airside buses. The Hal agent will check whether you have a bp or something to show you should be going that way.

And of course for the reasons noted by 13901, they are there to ensure no ones goes the other way so from international arrivals/connections in to the domestic arrivals area. If they did they could just walk out to landside and bypass immigration.