Is it a good idea to keep your magazines loaded? Will it damage or weaken the spring?
Correct. Springs will not take a "set" if you leave the mag loaded. It's the loading and unloading that weaken the spring and cause mag failures.Leaving them loaded won't reduce their performance in your lifetime. Constant loading and unloading will weaken them faster, though. Think about it. What will happen if you bend and unbend a piece of metal enough?