The ease of use for new users, especially those just getting into WordPress as well as experienced WP developers.
Also that you can do so much from one place! I would say there isn't anything I don't like about it; however, since we have an agency we are able to utilize multiple services at once. So if something changes or goes down elsewhere - not such a big deal. We get notifications when things go wrong via email directly from Accwf and from our plugin alerts us as soon as they occur and allows us to fix them immediately rather than waiting 24 hours which sometimes happens.