What year truck do you have? GMC or Chevrolet? 53-55 GMC and 54-55 Chevrolet trucks with an automatic Hydra-Matic)transmission did not have either a choke or a throttle cable (the vendor's rep might have had a hard time telling/selling you a correct length cable for those trucks).
My long-term experience is that cutting the cable to a short (exact fit) length decreases the useful life expectancy of a throttle/choke cable, especially if you will heavily use your truck. Over the life of a well-used truck, you will be removing and re-installing the carburetor every so often. Tightening, loosening, and retightening the cable-stops puts a bend in the cable and the cable will eventually break at the bend point. Then you have to trim back the cable.
If the cable is trimmed-to-length to start with, you will more quickly find the cable is too short. Yes, this will not happen soon on a truck that is not driven often. I do however think this is one reason why the cables are longer than needed when they are new (another reason is perhaps so the cables will fit on different sizes of trucks).
Leave a little slack in the cables when you measure them to be trimmed-to-fit.
