Are you answering an email on lilypond-user mailing list with some code that looks like an ugly hack but it works? Or maybe you think that your code is too specific to be of general interest?
Add it here anyway. Even if it really won't be usable to other people, it could be an inspiration. Or it could be improved later.
In general, almost everything can be added here -- if you think that your code is ugly or that the optimal solution should be implemented differently, just mention this in the description.