Any quality made spring will not wear out by being left loaded.
While this is certainly true, the difficulty is that there is no way to determine the difference between a quality made spring and one that isn't, UNTIL IT FAILS.
The quality spring lasts and lasts, the piece of crap spring fails "early".
But what is early?? weeks, months? certainly. A year? 3? 5? where do you draw your personal line?
I have personal experience with magazines left loaded 15 years. They worked normally when used. I've heard of magazines being left loaded 40+ years and working fine.
And, while I've heard stories of magazine springs that failed in a year or three, I've never personally experienced one.
The "Common Sense" of not storing a spring compressed under a load dates from the time of flint and caplock guns, where the springs were leaf springs,hand made by blacksmiths, which could, and would often take a set, or even break if stored under tension.
Modern coil springs are a much different matter.