The failure mode we see most in this town is someone trying to force the door open manually after a spring breaks, using the opener's manual release without knowing the door is now unbalanced. Without spring tension, an 8-foot double door can weigh well over a hundred pounds unsupported, and cranking it up by hand or letting an opener try to lift dead weight strains the opener's gears and can bend track.
The other place things go wrong is on doors where the spring failed months ago and got "fixed" with an extra loop of chain or a bungee cord holding tension - we've seen it, and it's a way to lose fingers, not a repair. If your door has been sitting like that, tell us before we arrive so we bring the right gear and clear the area first.
One honest limit: if the drums, shaft, or track on an older door are worn or bent from running unbalanced, a spring alone won't fix the door - that's a hardware repair on top of the spring, and we'll say so instead of billing you twice for the same visit.