Personally I try to rotate magazines about monthly. While I have kept Glock and AR mags loaded for over a year without issue but have had issues with other mags. Just don't see a downside to rotating them even though it's mostly just a forcing function to make me inspect mags regularly. Also I have been downloading mags for awhile now putting 14/15 or 16/17 in Glock mags and 28 into 30 round rifle mag. I think it gives just a little more push to keep things moving and both hold enough rounds that it shouldn't be an issue.
Do you rotate magazines?
What about loading them with a round or two less than the full capacity?