from everything I’ve read and understand about physics it’s what your friend is doing that will ruin the springs.
Springs wear out from use, not remaining either way statically.
That is, leave a mag loaded for 30 years, or empty for 30 years, and it’ll be fine… load and unload the thing daily it’s far far far more likely to wear the spring out (though it’ll still take a while with quality mags/springs).
See among many sources on this-
http://www.militaryphotos.net/forums/showthread.php?107014-Loaded-Magazine-Storage-Query&s=6f89e7bbee0f40d0b1351735ebc5ad4c&p=2358970&viewfull=1#post2358970