In the same way I look at my semi-annual "tune up" of my boat, during the winter months I take the time to really inspect my dock lines, even if I am using the boat and perhaps wintering in the Keys, as we did on Growler. When they get used while we are cruising, I admit I don't pay much attention to them, or check for the inevitable issues that can happen. Spend a couple of days at an old crusty marina, for example, and I'm not surprised to find wood splinters buried in the strands of the lines, often weeks later. We get under way, lines are coiled and placed out of sight in a locker, and no thought given to them until the next time they are needed.
But it is a good idea to occasionally take the time to uncoil these lines, put on some mechanics gloves, and run them carefully through your fingers to identify and remove any foreign matter than inevitably works into the braided or three-strand nylon. Your crew's hands will later thank you for it.
I also check for loose whipping or splices coming undone or loose. After I've checked all of my spare dock lines, I spend an hour or so with my sail repair kit. (It is in a tackle box I started assembling a millions years ago in Seattle that all began with a ball of Swedish tarred marline I just had to have for the sheer nautical smell! I found it at Captain's down on the waterfront, back in the mid-'70s. Over the years I added several versions of sailor's palm, fiddles, needles, and lots of bits of line, wax, and hooks. It is the kind of box old sailors get buried with.)
As you know, once three-strand nylon line begins to unravel, it is essential to take action to stop it as you lose inches then feet off the dock line, and it is all but impossible to fix that. Whip or seal the line and cut off the loose strands. You can later use these cutoff strands to make baggywrinkle for the rigging of your Tahiti ketch or whatever.
As they weather, dock lines can become quite stiff after years of use, so during this inspection cycle I like to soak them overnight in a bucket of water mixed with fabric softener. This does wonders to restore the flexibility and feel of the nylon. I do remember, however, to rinse and dry the lines before recoiling them and putting them away...or my locker smells like a laundry room.
Have a great week!