[birken]

Coincidentally I just had a professionally done garage door spring replacement today, and I asked the repairman this question, and here is what he said:

1. The springs lift the door from the bottom, and from each side, which puts less load on the door itself as compared to if the entire weight were being lifted from the top middle every time.

2. The motors can be smaller, quieter and use less power

3. In case of power failure, the door is much more functional and safer the less apparently weight it has.

Also the springs themselves are very unlikely to be dangerous (as long as you don't try to replace them yourself), because he said they almost always break when the door is at the closed state, because that is when they are under the most tension. Therefore on the whole, the springs in practice offer no practical safety risk, while greatly increasing the safety of the door in it's normal operation while also reducing wear and tear on the door. They also allow people to have heavier types of doors if they want them.