May you never have to write one again, but if you do, it might be helpful to think of the cover letter as a reflective writing exercise. You might be able to gauge your level of interest in a particular role by how easy it is to write about, for example. Or it could just be some practice at communicating your strengths and abilities (this would definitely apply to me).

IMO it's too disheartening to put effort into such personal writing without the awareness of some kind of direct value or benefit, since chances are it's going straight into the void.