That would accomplish nothing other than making Russia even more of an international pariah than it already is. They don't need to demonstrate that they can use nuclear weapons if they want to - the world already knows that.

The launch would almost certainly trigger a nuclear war.

The most likely use that wouldn't is to employ tactical nukes in Ukraine itself. On the other hand what would that achieve? There's no logistic hub or massed armour formation.

Nuke Kiev and Lviv for unconditional surrender. Worked in WW2 for the US. Personally not sure if it would work this time.