Importing a course: Only allows you to 'merge' some or all content from one location into another.
Backup and restore: Allows you to overwrite/delete the contents of a course prior to adding in the some or all content from a backup.
When you back up a course, you can select all or some of its contents to be part of the backup. When you restore that back up into another location, you can further decide to pull in the entire contents of the backup or further decide to select only a few items out of it.
If you're going to import contents from one course into several other courses, you can either (1) go through the 7 steps of the import process over and over, or (2) go through the 7 steps of the back up process just the one time. Then you can restore that backup into other courses (1 course at a time) but you don't have to go through all 7 steps each time.
I'm not familiar with Course Copy (Im' using 3.7). Hope that helps a little.