I agree, it is easier to get a new cable from a store, or work . But, I think if you are short on cash, repairing old cables could save you some money because some of those longer networking cables can cost $20 and more sometimes.
network cables are thankfully cheap, I rather get a new one than trying to fix it and screw it up. I have made cables in my cisco class, not a easy thing to do.
The short and regular cables are cheap, but longer cables which are electrical magnetically shielded network cables can cost more. Some network cables are sometimes installed inside walls, ceilings, and the floor like telephone and power cables, so sometimes replacing the plastic plug is simpler than replacing the whole cable which is installed inside a wall.
It is also sometimes hard to untangle network cables from a bunch of other cables, and network cables which may get tangled, so replacing a plug maybe easier if you know how to replace a plug.
I hate untangling wires as well. it seems the average computer has a lot of cables thesedays because of having so many wired stuff like power, network cables, keyboard, mouse, surround sound pc speakers, usb hard drive printer, microphone, Gaming mic headset, and headphones.