It's not going to harm the springs in any way to leave them cocked. There are many SxS and O/U shotguns that must be stored cocked (when taken apart and in their case) in order to get them back together.

Another example is carrying 1911 for personal protection. The only real way to carry that firearm and have it ready to fire is in the cocked and locked position. These guns can literaly spend nearly their entire storage time in the cocked position. If it damaged the springs in any way to carry like this many people would be dead becasue of it.