Very often on unix environment we have to deal with symlinks (aka soft links - reference to other files).
Because of different reason the referenced file may be moved or removed, but the symlink still points to the old file.
Such situations can lead to unexpected errors: e.g if your symlink points to an executable and the referenced file was deleted then you will get "Permission denied" message, and you will ask yourself: why it does not work ,couple of days ago it was just fine; and the file is there ?!.
Because of this few years ago I've made a small script to look for dead links.
Usually I start this script during weekend, and Monday morning I'm just looking on the reports.