> It might be silly if you're working on your own.

That's exactly the case when it's easiest. If you don't need a feature, just don't use it and case closed. With a team it's harder - you have to force/enforce others not to use a given feature.

> if they're used by libraries whose functionality you do want

If you're using C++ you can just use the C library you would've used otherwise, no?

There are linters to do that enforcement automatically.