Some good reasons.
Because of the flight characteristics of something like a "fly", they think that maybe surveillance "bugs" like that would be good for urban settings.
High lift, great maneuverability and endurance with a reasonable power source are parts of the advantage.
I read once that more "critters" fly than walk or swim. (Don't know for sure, but do know that a lot of them do in the later summer.) If that's close to true there has to be a very efficient way to fly we haven't discovered.
Arf