Insulating a garage door is most worthwhile when the garage is attached to your home, shares walls or ceilings with conditioned space, or is used as a workshop or gym where you spend time. It can improve comfort, reduce noise, and moderate temperature swings, but it also adds weight that may stress springs, tracks, and openers, and it is not a substitute for air sealing or an aging door. If your garage is detached, unheated, and used only for parking or storage, the payback is usually lower, and simpler measures like weatherstripping may be enough. Weigh your climate, door condition, budget, and how you use the space before deciding, and consult a qualified garage door technician for any mechanical modifications.