When that job is finished & you've exhausted a pot of coffee while daydreaming about the adventures you'll have with the new line, you look at your old line with nostalgia. Thanks for the good times, old friend.
Wait a minute. Maybe this isn't the end of the line (pun intended). Don't just throw away that old fly line because there's about a million uses for it. In fact, how you use this old fly line is limited only by your imagination.
First, you could easily make a lanyard for hanging all your fishing accessories (like clippers, tippet spools, etc) from. Hey, why buy one when you can make a perfectly good one yourself? What else do you have to do in the dead of winter? How about using a length of it to hang your sunglasses from?
Are you or someone you know into making crafts? Well fly line can be used for weaving baskets, bowels, etc. How about making a key chain from it. Craft making folks have vivid imaginations. You might be surprised with the ideas they invent for that old fly line of yours.
Of course I haven't even talked about the million uses it could have around the home. In the garage or the workshop I'll bet you could find a lot of uses for an old fly line. How about in the garden? I would think that some of the old line strung between two stakes in the ground would make a good trellis for your cucumbers or other vine-growing vegetables to climb up next summer.
So maybe it's not so long for that old fly line after all? Before you just throw it in the trash, stop & think about all the things it could be used for. You'll have the pride of being inventive & know that you're doing a good thing by recycling something that otherwise would have ended up in a landfill. How can you beat that?