When you click on 'Apply' on a jobsite where you've uploaded your CV etc, and the box comes up with a default 'covering letter' message to the recipient, do you go to town and actually bother with a 'covering letter' message, or do you just go with the flow of automation and leave it standard?

There are two main variations:

a) a job advertised by a recruitment agency
b) a job advertised by the actual company