There are so many applications within scuba diving where a diver will use a spool or reels. Most divers will use a simple reel or spool to deploy an SMB or DSMB on every dive they make. So having one that does what you need is really important. Knowing how to use it makes all the difference. For more advanced diving situations, such as overhead environments inside a wreck or a cave, lines are used to ensure divers can safely exit at the end of their dive.