[ftvy]

How much of an effect would linking shared / static libraries have on binary size?

Would someone writing assembly tend to avoid using external libraries unlike with HLL?

[ajxs]

Linking a static library into your program will increase your binary size, linking to a shared library will not. Smaller binary size is one of the benefits that shared libraries offer.

That decision is entirely up to the developer and the project requirements. If you're not writing a bare-metal program there's no reason why not to use external libraries. It's still perfectly possible.