I run it on an old Nexus 4 for shits and grins. Basically the only advantage that I can see (and the only reason I haven't wiped it off the Nexus) is I think the "hook the phone up to a monitor/keyboard and turn it into a computer" is the next big step in mobile computing. Whoever gets it right first will have the advantage. Microsoft is trying with Continuum, and Ubuntu has their version. Android has their home grown merging of ChromeOS/Android, plus third party things like RemixOS, and it looks like Apple are moving OSX and iOS closer to each other as well.
Odds are Ubuntu won't be the winner but its interesting to see where they're going with their phone OS.
Other than that, though, there's no compelling reason to use it. App ecosystem is basically barren, and there's nothing compelling about the UI to recommend it above all the other options.