An example to why you want to compare groups in EndNote is when you do the same literature search at different times. So lets say you did a literature search and you found 100 publications. Six months later you run  the search again, but you find 105 publications. How to identify those 5 new publications?

To do this you can use EndNote "Create from groups"

Make sure that the references are added to a group. I shall use the example in the introduction.

• The 100 publications first found are added to group "A".
• The 105 publications later found are added to group "B".
• Now go to Groups in the top of the screen and click 'Create From Groups'
  • This will make a new group, so first give it a name
  • Select Group B in the first slot
  • Select Group A in the second slot, and make sure the 'and' is changed to 'NOT'. 
  • Click create
• You will now have a group that has publications that are in Group B, but not in group A. So in this case, the group should only have 5 publications. Those are the 5 publications that were published in the time between your two searches. 

With "Create From Groups" there are also the options 'AND' and 'OR', with these functions you can create groups that have publications from other groups.