Applying for MS, what role should a cover letter have? I'm interested in applying for a MS in the natural sciences with professors some I have worked with in the past and other new ones. What role should a cover letter have as I reach out to these professors? My goal is to follow standard procedures but also not be excessive in my approach, thus I'm wondering whether to send one or not in the following context:

I'm not formally applying yet, rather I am early in the scoping process, reaching out to potential advisors to state my interest and request a meeting to discuss opportunities and options to work with them. I figure I will include my resume in an email reaching out to them, and that email itself is like a brief, informal cover letter. I have prepared a cover letter that I'd use in my formal application, but it is like a longer, more formal version of the email I'm sending to these professors.

Maybe for some or all cases it is more appropriate to send a cover letter and resume, letting those attached documents speak for themselves and keeping the email very brief? Some professors I'm reaching out to are people I cross paths with once or twice a month and am on a first-name basis with, some I have studied with in the past but they may only remember my face and not much else, and some I've never interacted with before.
A brife email with your attached CV is enough for information email communication with professors. unless you are applying formally to a MS program that define the length and the scope of the needed cover letter, you do not need to send one to your professors.