Many years ago I worked as a hiring manager for a PR firm in India, the cover letter is a very good way to sift out the dedicated candidates from the unfocused.

It also provides us with a unique insight into their psyche, using a combination of NLP and targeted interview questions regarding topics mentioned in the cover letter, we were able to discern potential points of leverage when it comes to salary negotiation. For example, an ideologically driven unior associate will accept a lower yearly salary as long as he's personal ego requirements are fulfilled, thus minimising operational expenditure for the business.