Adds checkboxes next to HIT links so that you can set a checkpoint. A checkpoint will notify you that you've already seen a HIT by changing the HIT link to display the date the checkpoint was set. A well-placed checkpoint is useful when browsing HITs by creation date (newest first) because it will alert you that you've already seen the checkpoint HIT and probably all the HITs that come after it. It's best to place a checkpoint on a HIT that won't be recreated because recreated HITs jump to the first page.
mmmturkeybacon Color Coded Search with Checkpoints has the same functionality built-in. So if you have that installed you don't need this script.