The point of it
It is fairly common for a concordance to show you repeated wordings: you may wonder whether your corpus contains unwanted repetition.
How to do it
With a concordance on screen, choose Edit | Remove duplicates in the menu. If there are duplicates, you will find the last one marked for deletion. You can prowl up and down the duplicates so found using the < and > buttons.
The procedure seeks out concordance lines where all the words within the current collocation horizons (fefault: 5L to 5R) are identical, and then marks one copy for deletion.
The line above is only in the first 11% of the text; the one below is more than half way through the text.
See also: duplicate corpus contents.