100% control of the supply of gas to some parts of Europe. Those countries, being in the EU, means Russia cannot utilize its full capabilities as a monopolist. The EU represents a monopsony on Russian energy to the west. They aren't selling to individual nation states, they are selling to a single bloc with a unified policy. Putin was already trying to entice European countries to break away during the last EU crisis.

If the EU fragments, Russia can better maximize their profits.