There is nothing wrong with leaving mags fully loaded. Springs only develop problems by "cycling", (lots of use) someone trying to cram 17rds in a 15rd mag for example. If leaving mas loaded was a real problem, it would be widespread thru every L/E agency and in every part of the military. This is not the case.
"Some People Are Like Slinkies. They're Not Really Good For Anything, But They Bring a Smile To Your Face When Pushed Down The Stairs."