I'm totally against coverletters. I have NEVER seen where they make a difference.
They are supposed to be a quick summary of why you are a good fit for a job. Most CVs are very word condensed documents most people will have 1-2 pages maybe even more depending on your portfolio. Do you think top engineering jobs will hire anyone with a 1-page CV regardless of the credentials of the individual?
A cover letter is designed to quickly summarise your skills and how you will be a good fit for the position, a good fit for the organisation and what values you could bring to the table that they might not have or are in need more of.
Employers will take a quick glance over your covering letter to see if you fit the bill. So instead of an employers spending a minute or two combing through your CV they would spend seconds and that is the difference.
Do you want them to see the skills that you have glaring right at them or do you want them to take the time to read everything in your CV to see if you are fit. They would most likely appreciate the time you took to make their job easier.
If you don't need it then fine but for me and others a good covering letter is usually what I feel gets me at least into the door for an interview.