I grew up learning without a leash, due to tough guy protocol. It definitely helps you become a better waterman and have more control of your board. Lots less drag on small days. When it is sharky however, it gives you a whole new perspective. And during a sharknado event, with a leash the board can tend to slap you around a few times before the sharks get you, kind of like pre tenderizing the meat.

On crowded days, I think it is the responsible thing to do, unless you can blast insane airs and never lose your board. I wear one, unless I am longboarding on a clean day in less crowded conditions. I've snapped a couple duck diving huge sets, which really sucks.

Sometimes you need one. Almost died swimming back in at the Point in Dominical after an ill fated duck dive way outside on a dropping tide trying to make it over a clean up set on a very big day. Body surfing over shallow boulders to get back in was hairball. Should have used a brand new leash that day. Also, I've been tombstoned on big days and pulled myself up with my leash. Once though I unknowingly pulled my self down, then had to push off the bottom with just about no breath left. Same thing that makes you laugh, makes you cry!