If your garage door is standard aluminum less than 10 feet wide than almost always requires only 1 spring, compare to a same size wood door that normally has 2 springs. The most common 2 car garage door is 15-16 feet wide. These doors can use only one spring also but most common they have 2 springs.

There are pro’s and con’s with both single spring and double springs

When single springs break the door will not open without at least two good size men. This means you know there is a problem with your garage door. If you have double springs and one is broken than the good spring can make it easier to get door open to remove cars etc.. Now some garage door openers will be able to open a door with one broken spring. This can seriously wear on opener parts. And the thing is you may not know you have a broken spring and will eventually ruin your opener. So this will be your decision.

Anytime I am asked this question I just tell them what I just explained. You can go either way so just be aware and routinely look over your garage door for broken parts.