Ardour is an amazing piece of software, but sometimes it still crashes. This is not entirely its own fault - plugins have to run in the same process so ultimately Ardour has no control over some of the code it ends up running. I find it pretty stable, but when you are syncing it with MuseScore and/or video things get a bit twitchy.

Of course, we all know to save early, save often - but when you're in the creative flow it's easy to lose track of time and not save for quite some time.