It's a safe way to mark off your quilt without making actual marks on it.  

It's marked off into quarter inch increments.  You can keep re-using it until it doesn't stick anymore.  

You can use it in conjunction with your rulers. For example, you can cut the strips and place them on the quilt to make a 10 inch square.  Then use those 1/4 markings on the tape to determine where to place your rulers for cross hatching.