So I imagine you can get a pretty solid backup just by using SQLite tools on that one file (though backing up the entire Plex Media Server folder might also be nice to do every now and then to save other things such as plug-in data).
The DB, although obviously undocumented, is also an interesting place to poke around for looking at the data for your own purposes. For instance, it looks like the statistics_media table stores your watched show history.
I haven't tried to restore, but I keep the backup in a separate location.
I guess it's because I don't use (or see the need, really) for these features. I mean, I can remember fine what I've already seen and I don't mind clicking through to my next episode when I get back into Plex, and I don't really care to know what I've watched in the past, how many times, or how I rated it.
I'm more bothered by its DLNA server crashing, its occasional screw-ups with multi-audio or multi-subtitle containers, or it's failure to transcode some files (though most of these might be due to the receiver more than Plex).