Not the parent commenter, but I'd assume it's mainly browser sync.
Being able to log into any Chromebook and immediately have all yours bookmarks/apps/tools/passwords/etc. that you use on your desktop and laptop is pretty useful.
As great as Firefox is, if you use Chromebooks then you're gonna use, well, Chrome.
Eh, I use Chromebooks occasionally. The trick is just to not lock things like bookmarks and passwords into you browser. 1password and pinboard both work great with Chrome.
