Yes, I’ve also been told that cycling is what wears out the springs. Still, I keep 28 rounds loaded in my 30-rd. AR mags and I load my Glock mags 2 rounds AHT of full capacity. For my EDC gun (p365 XL) I keep one round shy of full.Leaving them loaded doesn't hurt them at all. Many download a few rounds from full but I don't bother. It does take some stress off the feed lips though.
Cycling the springs is what wears them out. Full, empty, or somewhere in between doesn't.