In my neck of the woods, we fish single and we fish barbless. In fact, it's now the only way I roll.

Without a barb to hold that hook in place, the angler MUST keep constant tension on the fish 100% of the time or risk having the hook back out of the puncture site. Some anglers can do it, but MANY simply can't.

With a smooth curvelinear bend and no barb, the hook can very easily follow its tract in reverse back out thru the original puncture site. With ZERO resistance along a smooth round bend, there's nothing to help keep it from backing out with simple rotation.

With the sickle bend, the sharp acute bend at the bottom of the "J" serves to effectively "lock" that hook in place once it has been set by the angler. The hook resists backing out with simple rotation, esp if it finds a solid bony purchase.