It was probably 19 or 20 years ago when I first learned the importance of using a bite tippet. I was on vacation with my family on Florida's east coast doing some barracuda fishing from an inlet jetty. Armed with a spinning rod and a bunch of medium-sized plugs, I walked out to the end of the rocks, found a nice flat one to stand on, and began casting a big Rapala tied directly to 15-pound test (big mistake). While violently ripping the lure back on about my third retrieve a big cuda—easily 20 pounds or more—absolutely SMASHED the plug. I set the hook hard and the reel began to ziiiiiing as the fish peeled off southbound. I don't think I even had a chance to get out my third cuss word when the line parted ways with a clean slice. The fish and my brand-new plug was gone! In the next hour or so, I went on to donate two more plugs to those toothy critters before leaving in utter defeat. I vowed to return the next day better prepared!
Help prevent similar defeat from happening to you by using a bite tippet, or as some call it, a shock tippet. What is it? It's simply a short piece of heavier line or wire added to the end of your existing tippet (aka the "class tippet") to protect from things like sharp teeth or abrasions. While many freshwater anglers may never need to use a bite tippet, a lot of saltwater pursuits pretty much require their usage.
As an example, we'll take a fish I target heavily for about half the year—snook. They have abrasive mouths and sharp gill plates, both capable of easily fraying or slicing light line. My typical snook leader for beach fishing near home has a main body consisting of a 9 or 10 foot length tapering down to a 12-pound test tippet. However, rather than tying my fly directly to this 12-pound tippet, I'll first tie a short piece of 20 to 30-pound fluorocarbon to the tippet, then tie my fly to the other end of this heavier line. This heavier line is my bite tippet and will be able to better withstand rubbing on the abrasive mouth and gill plates. Without it, the 12-pound line tied directly to the fly would be much more susceptible to damage and failure.
The length of shock/bite tippet can vary based on the species you're targeting. For my snook fishing example, I usually stick with a pretty small piece of maybe 8–10 inches. The fish are generally smaller in size and this length is long enough to both protect from the abrasive head/gill area while still offering the "stealth" of a short length. For bigger fish like sharks or tarpon that have a much larger mouth or head (the "danger zone" as I call it), a 2-foot or longer shock/bite tippet may be more appropriate.
Off the top of my head, some common species that you'd likely want to use a shock/bite tippet for would be pike, musky, shark, barracuda, snook, and tarpon. It's amazing how abrasive a fish can be to your tippet. Even after catching a little 16-inch snook, my heavy bite tippet is often scuffed up and needs to be shortened and the fly tied back on. While that can be a bit of a pain in the butt, it's far better than losing the fish. With that said, don't think that using a bite tippet always guarantees you'll land the fish, but it surely tips the odds in your favor!