Convenient
Its very convenient to be able to keep Facebook as a desktop app thats separate from my web browser. I access it via a keyboard shortcut, so I spend less time fiddling with browser tabs to get to it. And it also acts as a messaging app, so I can leave it running in the back and quickly toggle back and forth between FB and other things. There is much less friction with this app.
CyberK.S. about
Go for Facebook - Unofficial