A secondary benefit of the fishing swivel is that it may function as a stopper for sliding sinkers, which depending on fishing method may be placed before or after the swivel. Three-way swivels provide an additional ring that serves as a point of connection for side-branching line segments, which are essential for certain line and hook setups.
The main purpose of the swivel is to allow the two line sections to rotate independently of each other, which allows self-unwinding of any twists formed during line casting and retrieval, preventing undesirable tanglings. This is particularly important for users of monofilament fishing lines that tend to express memory and form coils when released from a fixed-spool reel.