I once (long before I ever knew of paracord) had about 10 feet of nylon string in my kit and it was enough to tie the two inner tubes together that I had decided on a whim I would float down a river on, and to have a drag handle, and also to make a new bootlace when one broke. I didn't need any other corgade to last me those few days;
But if I had planned to be using a tarp or something that requires it, I would have carried more. I hadn't packed it because I knew I'd use it, but it made the inner tubing possible, so I'm glad it was there.

Sometimes you don't know when you will need some string; and if its versatility is the number one reason why you carry it, carry some in your "what-if" kit, I suggest 50 feet of paracord...This amount does not include the amounts and lengths that you already can account for using specifically, and should be more than enough for any whimsy or ingenuity or bootlace mishap.

Only take more than a reasonable amount of "what-if" cordage if you anticipate actually using it. It makes no sense to waste valuable kit space carrying something that will never be of any use to you.

If you think you might need cordage longer than about 50 feet, you might want to ask yourself specifically why. You might actually need to sign up for a rappeling class. Never try to rappel with paracord.

Also, proficiency with cordage includes a multitute of knots for different purposes, and your proficiency with cordage should be able to clearly enable you to know how much of what kinds of cordage you might need for any specific purpose.

Paracord is never included in a kit for its intended purpose, so any more than 50 or 100 feet (expeditionary kits) in addition to how much you know you will use, is absolute nonsense.