A strong cover letter can make a very good first impression. Your CV has limitations, so this is the perfect opportunity to inject some personality into your application and tell an employer a little more about yourself. Don’t go overboard and keep the cover note concise and short, anything too long is unlikely to be read.
In terms of the content, the cover note should show enthusiasm and passion and conclude on an action such as ‘thank you for taking the time to review my CV and I do hope we get to discuss the job in the near future’. You need to give an employer a reason to open your CV and a cover note allows you to personalise your application.