"Good" foilers have foiled MANY days, so have experience and have tried different setups.
Most bad foilers are less experienced, tried fewer setups less days, and have limited knowledge.
Me? Don't matter. I am a newbie, but have seen and talked to a dozen wingers who surfsail in 5+ foot shorebreak, jump both directions in surf, and considered EXPERT by anyone.
However I do have 25 years expert surfing experience, and coul leashes are NOT for breaking sur conditions.
As for a wing leash....yes, if you want, but be aware the coil makes a flagging wing much harder to control, and you need control of the wing when it's down. You don't need to ask why.