Swivels generally serve two functions. First and foremost, they are there to reduce the opportunity for your line to twist. This is particularly true when casting baits into the surf or dropping them into the depths. Rigs will often be moved and twisted around by the water movement and the action of the hooked fish. Retrieving twisted line onto your reel over a period of time can build up and impact on your fishing in a range of ways. It will decease your casting distance or worse it will catch on the rod guides causing the line to snap and your terminal tackle to disappear over the horizon. The second function of the swivel is to join the main line to the leader material of your choice. It is the easiest way for most anglers to connect lines of different breaking strains. A swivel can also prevent the sinker from sitting directly atop the bait allowing for a more natural presentation in some rigs. Swivels are an integral part of every angler's tackle kit, from offshore reefs to inland rivers and lakes.