When creating a course enrolment key, you can click on the reveal eye to see the key (shown on right of attached image). 

However, if an enrolment key is used at the course level, the student cannot see the reveal eye (shown on left side of attached image). Not everyone thinks of copy/paste, so we get a lot of people trying to type the key, and a number get it wrong, from which we receive a Help ticket. A fairly significant amount of time would be eliminated with the addition of this feature to core Moodle.

Cheers, Neil