What are the benefits of external libraries vs embedded.
No functional difference, however, embedded libraries ensure users have a seamless experience with one addon install instead of having to install separate libraries themselves. If they use the Curse client and choose to install libraries separately, again no function difference. The way libraries work, the newest version found, whether or not it's embedded somewhere or installed separately, will be the instance used.
No one really uses external/standalone libraries unless you need to e.g. debug a library's memory usage