Why does aluminium sliding door have a section that sticks out?

Scootergirl

My late 80s townhouse has sliding glass aluminium doors and they all have this annoying bit that protrudes about 3.5 cm from the rest of the door; and sticks out about 1cm further than the architraves. I can’t see any use for it - does anyone know what it is and why it’s there? 
It’s annoying because I’d like to instal roller blinds but they’d have to sit out from the architrave to clear this.

Probably a silly question but would there be any way to remove it? 

JDE

Scootergirl

Ive never seen a sliding glass door without it or an equivalent tube. I would avoid removing it as it adds structural strength to the door and stops it from flexing in the middle. Which in turn stops the glass flexing and breaking. You could always attach a pelmet to the top of the facia above the door and hang your blind from inside it, this gives better insulation as the pelmet stops the movement of air. 

James