Any time it's not super well explained, I just always assume FTL engines are utilizing some method of spacial distortion rather than actually accelerating an object to such speeds. Like I kind of feel like if you plot a course and there's a planet in between you and your target coordinate you'll just most likely go "through" it via kinda going around it through spacial fuckery

The Expanse had the belters launch asteroids to effectively nuke parts of earth

There are stories that use it. The term "relativistic kill vehicle" gets used sometimes. Spin a rock up to a good fraction of c then delete a whole planet. Really depends on what the writer wants to do, though. Three Body Problem is the most recent famous example of "ftl big gun." Thing. Star wars has done it a bunch of times. One of the old comics had a star destroyer that fired planet cracker torpedoes through hyperspace. The ancient Lensman series has had every kind of variation of "strap ftl drive to object" you could imagine.wh40k orks hollow out asteroids, fit them with warp drives, then fire them at the next star system they want to invade. They crash the entire asteroid, or moon, in to the target planet as their invasion ship.

In practical terms there's very little reason to destroy an entire planet. It's complete overkill. You can decimate the population of a planet but things like farmland and living biospheres are in short supply in the cosmos, sublight asteroid drops do the job just fine and you can just wait for the dust to settle and sift through the ruins for valuables

It’s a divisivr movie , but that exact scene in The Last Jedi fucking rocks

That's assuming that an engine built for driving a space ship would be powerful enough to push the giant space rock.

It'd be like strapping a car engine to a mountain and expecting it to go just as fast.

I recommend an obscure, fun, bonkers SF novel called The Killing Star, which features accelerating metal slugs to 90% c before flinging them into planets. There's also a chapter that takes place on the Titanic. And TNG makes an appearance toward the end. Supposedly the ships in this novel inspired the interstellar vehicles we see in the Avatar movies. There's also an earlier book in this series which features wooden spaceships piloted by kangaroos (though it's all hard SF, I assure you!).

Depends on how much effort it is to add the engine to an asteroid. Besides that, it would be single use and the navigation system of the ftl is probably not precise enough to hit a ship/station several LY/AU away.

Stargate SG-1 did something similar. It was a wormhole having subtle effects on an asteroid's trajectory that just happened to aim it at a planet, but the asteroid was initially put in the path of said wormhole by the Big Bad. This is followed by Bombs Not Food trying to save the day, failing, and the in-universe version of deus ex machina.

Somewhat similar concept on a TNG episode New Ground, they test a new warp magic device that creates a warp wave and after a failure they unintentionally discover the wave will destroy most of the planet.

Build one of these a few light years away from a nearby enemy planet and boom.