The cover letter is essential for me as a hiring manager. When I have a pool of ~100 applicants for a graduate role, I need something to differentiate between the candidates beyond the list of courses they've undertaken and summer jobs they've had. I'll filter first on only those applications that have cover letters attached.
Any cover letter shows that they're willing to put the effort into applying rather than just spraying the same CV to lots of employers, but a good one shows that they've researched my company and are motivated to work there. Doesn't need to be in great depth, but a line talking about one of our products and how its use in a specific industry is interesting to the applicant speaks volumes.
There are bad cover letters too, including those written for a different company but carelessly sent to mine...
I've never had HR send me anything but the resume when I've been involved in hiring. For that matter, I don't know that I've ever sent anything other than a resume in forty years of working in IT.
Same, but the value/need for a cover letter partly depends on size of organization, sector, etc. I know very large firms that use something like LinkedIn for job applications and automate the initial screen through that/resume-only. I tend to work in management with sub-100-employee companies and prefer having a cover letter as part of the hiring process, which is also more manual.
Any cover letter shows that they're willing to put the effort into applying rather than just spraying the same CV to lots of employers, but a good one shows that they've researched my company and are motivated to work there. Doesn't need to be in great depth, but a line talking about one of our products and how its use in a specific industry is interesting to the applicant speaks volumes.
There are bad cover letters too, including those written for a different company but carelessly sent to mine...