Could someone spell out for me what twisting/untwisting the cable and string does?

Like:
Twisting the cable 1/2" shorter = ??
Twisting the cable and string 1/2" shorter = ??
Twisting the string 1/2" shorter = ??

Or something like that.

I've read different posts until I'm nearly brain fogged and still can't get it. Basically I want to take 1/4" out of my DL without changing my loop but I'm also trying to learn the principle behind it.