This is pure terrorism, which benefits Russia in many ways. Strategically, it diverts a lot of Ukrainian resources towards protecting and evacuating civilians from areas where they should be pretty safe, away from the front lines. Russia wants to disrupt Ukraine's advantages on the battlefield (better training, better equipment, higher morale, stronger will to fight) by keeping them spread thinly and reacting to civilian catastrophes.

Attacking civilian populations is a war crime for good reason: it's effective and is a cheap/obvious strategy for anyone who does not care if the enemy population lives or dies. It's for truly evil people.