It lets you see that eraser is working. Try it
1) Select wipe method - eg 7 pass wipe
2) select a file to wipe
3) Start wiping
The verifier will open up the file in a hex editor view allowing you to see the contents. Pressing continue will perform the first pass of the wipe process and then show you the contents of the file after the first wipe. Assuming the wipe worked you will see that the contents of the file have changed to either random data or a set pattern. Press continue again and the contents should change again and so on until you've performed the number of wipes you selected.
If for any reason the contents do not change it means that eraser did not work