Why does my vacuum cleaner have a flap just inside the entry to hose?

My vacuum (hoover bagless) had no suction so I turned it over and found a mess of a clog just behind the beater bar. I took it apart and cleaned it out and found there is a flap just at the beginning of the hose. I pushed it with a screw driver and it does move open but not easily. I have to push pretty hard to get it to move. Does anyone know what function this flap has? Can I remove it somehow or would that ruin my vacuum?