If you have a dependency with 1,000 LoC and your application is utilizing 800 of them, that seems like a good reason to use the dependency.
You're (hopefully) getting unit tests, documentation, and public exposure of the code (bugfix opportunities) for "free"
If you have a dependency with 1,000,000 LoC and you only need 1,000, that indicates the dependency isn't a good fit for your project.
This is only a heuristic, but are there any tools that examine metrics like that?