The light elastic can be used for binding soft baits like crab and shellfish whereas the heavy elastic is best used for binding bigger baits. Helps to keep hook points clear for better presentation. Can easily be removed by hand and is more resilient to deterioration than other elastics.
REVIEW IN TOTAL SEA FISHING (JUNE 2008) - "This is one of those items that should be in everyones tackle bag. You have the heavy elastic for binding big baits for cod, bull huss and congers to give better presentation, and the light elastic for smaller soft baits like crab and shellfish. This is not only to make it more secure on the hook but also to streamline baits when casting any distance."