You can do things like decompiling a program piece by piece like the Ship of Theseus. The linker will mend both original and rewritten parts together into a working executable at each step.

If you change the functionality of the rewritten parts, you have a modding framework that's far more malleable than what traditional binary patching allows.

As for quick one-shot jobs, I've created an assert extractor for a PlayStation video game by stuffing its archive code inside a Linux MIPS executable and calling into it, without figuring out the proprietary archive format or how the code inside the delinked object file actually works.