[PvK]

I've seen several battles where drones were decisive. Sure they take research and are expensive, but they're not expensive in the long run since they have zero maintenance cost. They can also give you the crucial element of surprise, single a single ship, even a transport, can launch many drones, and many people are not expecting drones. They can be good for scout and suicide missions because losing them doesn't give enemy experience nor your own empire a happiness hit. Etc. They are a bit tricky to take good advantage of, and you can certainly waste a lot of time/energy/resources/research doing inefficient things with them, but they can be used to good effect.

PvK