There's one useful purpose to the HD code. If there are several different releases of the film or episode, there could be synch issues if you choose the wrong set of titles. The HD at least helps to decide if "this particular" set of titles is the one that fits the release.

Well, whatever suits you...
But don't you worry about the consequences of a mechanical failure of your hard drive? Or do you use backup array or something similar?

I don't, in a sense. I build "dvd-size" folders, numbered consecutively from 0000 on up. Each directory holds 4.3 gigs of movies, or as close as I can get to it. NOW...each time I build a new folder, the films stored in it get the folder number. So, if "black swan" went into 0178...