Big collection of heat shrink tubing
Chemical resistant
UV resistant
Waterproof
Flame retardant 
Lower applied cost
Reduce operating time
Strain relief for connectors and splices, providing more flexibility
Protection against harsh environments such as abrasion, UV, and chemicals
Sealing to keep out moisture, water, bacteria, mold, fuels, and more
Insulation protects and minimizes heat transfer for solid thermal and electrical insulation
Cosmetic improves organization of wires and overall assembly appearance
Color differentiation to help identify wires for color coding
Displacement of glass, tape or glue
Available in different colors, sizes and price ranges accordingly