I like how it's simple to set up with no configuration needed at all apart from some environment variables (which are easy enough).
It has made deploying new code much faster than before - we used Apache/mod_wsgi previously but this is so quick that now our developers don't even need root access anymore! As an added bonus you can use Nginx as well which makes life easier in certain situations too :) The logging system could be improved by adding more options or customising where logs go etc., however these issues aren’t significant problems compared against other benefits of using passenger such speedup deployment times without needing any extra setup work required prior when running apache2 mod-php applications via wampserver / xampp was necessary.