Cheap compact off-the-shelf computers and improvements in battery technology has only made guerrilla wars much harder for empires. It's not that long ago that if you wanted to do recon of superior enemy forces, you needed to put people in eyeshot of them, or maybe if you were really fancy you could jury-rig something stationary with a camcorder. Nowadays you do a flyby with your Mavic Pro knock-off from a reasonably safe distance. And you can do it over terrain that's normally impossible for regular people to cross, like wide gorges and raging rivers and minefields. Having the enemy waste munitions in shooting the drone down (if they even spot it) is only a bonus, because every round fired at a disposable drone is a round not being fired at your own fighters.