We always use heat shrink tubing for neat, professional solder joint insulation. With a heat-gun or a flame, it shrinks to a tight fit.
Heat shrink tubing guards against short circuits and keeps a guitar's control cavity tidy, unlike gummy electrical tapes. Always needed, and especially useful for complicated circuits with lots of loose wires.
Polyolefin shrink tubing has a low shrink temperature, yet is tough enough to resist damage from high heat. The thin walls reduce bulk, which is very helpful in tight places. Resistant to common fluids and solvents.
This assortment includes 158 pieces, 2-1/2" long, in a convenient variety of sizes: