An important use of a logging facade is when you're writing a library. Embedding dependencies in a library is always something that requires a bit of care, and logging even more so.
In short, you don't want to force your logging implementation onto your library users. Using a well-chosen facade means they'll be able to handle your library's logs with their own framework of choice and won't have to go through some weird dependency exclusions and loopholes to make both your logging framework and theirs coexist.
