I keep some magazines loaded.

I recently found a WWII 1911 mag that I loaded in 1974. It worked fine when I fired the rounds from it.

Poor quality magazines like Triple K and Promag and unknown makes, I wouldn't trust at all.
As long as you have good quality springs they don't fatique under constant load. I keep some replacement springs around just in case.

Some aftermarket springs are too strong (Wolff 11 lb 1911 springs) and will spread feed lips. Aluminum mags can also have this problem as previously mentioned.