I'm preparing to submit a math paper to a good general-interest journal. The page asks for a cover letter. What should this include, beyond "here's a paper for consideration"? Should there be, for example, a brief summary? Claims about why I think it's interesting? Suggested reviewers? The first two of these of course appear in the article. The journal submission page gives no guidance.
This is a near-dupe of Are cover letters sent to referees and should you highlight the contribution of your paper in the cover letter?. However, Googling around suggests that the answer is rather field-dependent, and this is not reflected in the answers there. I am looking for information relevant to pure math, for which a search hasn't turned up anything.
In my previous submissions I've basically blown this off, per my adviser's advice. It doesn't seem to have caused any problems, but I'm wondering if there's anything I can do to make the editor's life easier.