In flight rubbish disposal, yes, but only for appropriate rubbish. Banana peels, apple cores, handkerchiefs filled with vomit. Definitely not cans of drink or plastic bags.
Excellent ventilation as a Delayed Vomit window, though Cessna's windows do work better.
Great for the refueller to poke the docket for your last refuelling, through, when there's no one at the plane.
Great for flour bombing in flight, and Aerial Golf.
Would be great for throwing out the toilet roll for a spot of streamer cutting, if the Warrior was a good aircraft for streamer-cutting in.
Flying around the desert, your cabin will fill up with flies on the ground. The little window is a great way of getting rid of the flies. All you need is a short length of flexible hose. Put one end of the hose out the window, and use the other end like a vacuum cleaner. Chase the flies around the dashboard, and as they get close to the end of the hose, sluuuurp! They're gone!