This is one dad taught me long ago and it’s particularly handy with braided line. Braided fishing line can be pretty expensive. So naturally it’s rarely a good idea to put it on a reel starting all the way down at the spool.
Instead, I’ll use monofilament as backing for braided line; putting several feet of mono on the spool first and then tying my braid onto that backing to finish spooling the reel. But you have to make sure there’s enough braid on the reel to cover the knot well where it’s joined to the mono. Otherwise, when you go to cast you’ll feel the knot and it will negatively impact the efficiency of your cast.
So what you end up with is half your braid near the top of the spool seeing a good bit of sunshine and use while the braid below never sees the light of day. This is actually a good thing though and gives you an opportunity to get twice the life out of your braid by simply flipping it. By “flipping” the braid, I mean getting the fresher line that’s on the bottom to the top and the worn line that’s on top down to the bottom. You can do this a couple different ways.
If you have an empty reel, simply run a little backing onto it, tie on the end of your braid coming out of the reel you’ve been using and then reel the line off the old reel onto the new one. This leaves you with the fresh braid at the top of the reel and the older braid down below where it will never again see the light of day or any strain. If you don’t have an extra reel but you do have a clean grassy area, you can take the old end of the line and peel it off your reel by walking out into the grass, then wrap it around something really smooth and walk the end back to the reel. Then cut the end of the braid that was tied to the backing, tie the used end to the backing and reel your line back in to fill the spool.
Flipping your line works really with braid but not as well with fluorocarbon and monofilament as those two lines have a tendency to dig into themselves and damage the line nearer to the spool. Reeling line from one reel to another also works better with baitcasters than spinning reels; spinning reels tend to get line twists if you try to reel from one to the other. But you can walk your line out and flip it with a spinning reel as well.