Experts believe that the Russians use Iranian drones exclusively to terrorize the Ukrainian population

This is reported by experts from the American Institute for the Study of War (ISW).

In their opinion, there is no practical benefit from Shahed-136 drones and they are unlikely to significantly affect the course of the war.

Most often, the Russians use drones to hit civilian targets behind Ukrainian lines. It says that they are simply terrorizing the population.

ISW also writes that Russian troops seem to have already used a non-trivial percentage of Shahed-136 deliveries, if the claims about "hundreds" of drones provided to Russia are correct.