A safety reel (or spool) properly used can absolutely eliminate getting lost in low visibility. For example, you can tie off on the anchor line and run your safety line to the site - and if you miss the site you can get back to the anchor line by using your safety line even if the current or a piece of steel shipwreck that screws up your compass messes with your brain's picture of where you are.Butch103 once bubbled...
I have never carried one ( right or wrong) so I am curious. For the surface marker?
Everyone I know who has actually carried and used a safety reel a few times won't dive without one now.
E. itajara
PS Oh, yes, you can use one to send up a marker from your safety stop too if you want to. (a spool's easier to use for this)