I use this to give students credit for assignments that are done but do not need to be collected for grading. It's more like participation. I give 5 points for each stamp and if printed on both sides gives space for up to 50 assignments. I copy it onto cardstock and it is good for the whole year. When a row is full I collect and they get points for what is stamped.
When an assignment is to be stamped I come around check it for completeness and give them a chance for questions. I stamp both the card and the assignment. This way they know not to try to turn in the assignment later.
Cuts down on grading a lot of little things that done need it. Especially things we have gone over as a class already.