If they are USGI or better load them up and leave them. Can't comment on the cheap ones.
And before someone brings it up: load 30 rounds in a 30 round mag, not 28, not 29...
I would have to disagree with this. In fact strongly. Quite often a factory magaizine with 30 rounds will fail to seat properly or will be exceedingly difficult at an inopportune moment. Downloading by two rounds completely eliminates this issue and ensures smooth, speedy reloads, regardless of if the bolt is locked to the rear or forward.
This holds true no matter which continent you are on...