That's true; however, in GNU/Linux, the solution to this is one "rm *.xmp" away - so, not a problem if I don't want to have themDarktable isn't a go for me. I remember why I dumped it last time (apart from it not being enough for me). Every time I accessed a new folder, it dropped XMP sidecar files in there and I do not want to see them.
On a more serious note, I realise that not everyone likes or wants to do that - it's a nuisance, that's for sure. On the other hand, the XMP file means that I get to keep basic information about the file intact while editing - thus, starting over is no problem. But I guess that's the case with most applications today, anyway ... I won't evangelise Darktable, though. It just happens to be a piece of software I know how to work with quite efficiently, and I like that. My feeling is that it's on the way to become quite powerful, too, but it's nowhere near the GIMP in absolute terms. It's sufficient for my needs, though.