These units can bombard terrain enhancements such as mines and farms, reducing the resource production of the target and starving out the populace. They can also destroy roads so your opponent cannot reinforce a threatened area. Causing a drone riot right before an invasion serves two purposes. First, units supported by a base in drone riots fight with a morale penalty. Second, a base with drone riots cannot produce new defenders, and must be resupplied from somewhere else.
Thoughtful leaders utilize a mix of the four that changes each game in response to their situations.