There really shouldn’t be any debate about this. Wear a leash. Let me say it again: wear a freaking leash. Or, if you don’t, then stay away from me. This is from sup global:
A leash will stop your board running away and hitting someone else when you fall off. Stand up paddle boards are big things and could seriously injure somebody if they hit them. A leash is an essential.
You need to make sure that your leash is about 1ft longer than your board if you are going to do cool stuff like nose riding (otherwise you won’t make it to the end of the board !). If you know you are falling off, or if you bail out intentionally because a big wave is coming that you can’t make it over, try and grab the leash as close to the board as possible, this means that you control, as much as possible, the board in the surf, preventing it from racing off and potentially hitting someone else. If you are going to surf please avoid the coiled XM leashes. While they are perfect for distance paddling they are dangerous in the surf as they get tangled up, making the leash shorter and the board more likely to fly back and hit you.