Always two sides.. There are a number of commercially available products. I would never recommend a leash with little or no give - say a surf board tether they are too short.
1) I have used a reel leash for 6 years (guess it has 2.5 to 3 metres length on reel)) - not hit by board once - not lost a board either (twin tips only). By the time the leash has un-reeled I have stopped / almost stopped when I crash.
2) I always use a helmet (Gath) as luck does not come into it - the board could hit you.
3) I always take the leash off when mucking about trying aerials and if waves are steep - I do not have the skill / desire to go for big waves.
4) I do not go out in extreme conditions.
5) In tidal zones / river mouths - high water flow zones leashes are great.
6) The more experienced you are the less you are likely to need a leash.
7) The more you practise body dragging the easier it becomes.
Look at the lost and found - lost board covers a big % - a leash removes this problem.
I could go on - I found it great to learn with reel leash.
SF
no no no
