Limiting fuel = limiting assaults. At the very least this stops any attempt at a spring offensive in the region for Russia.

If Ukraine can limit access to fuel across the entire front the invasion collapses. An army without fuel quickly runs out of food and ammo.

If they can limit fuel availability across the entire country for long enough, Russia's economy collapses.

Ukraine apparently has some long range drones that pack a larger amount of explosives. Previously Ukraine was aiming at the the delicate portions of Russian refineries with smaller drones. This year they are hitting the main storage tanks (If I am reading the specs right, the crude oil tanks have steel walls 10-30mm thick).

I anticipate Ukraine to keep up the pressure this year by obliterating some oil refineries.

Best case is capture them thus adding more equipment to the Ukrainian military. This is hard though, sometimes risks too many lives to be worth trying.