Taking one or two rounds out will reduce the stress on the springs. Also, I'd advise rotating your loaded mags. As has been mentioned, it's a topic where there are a lot of opinions so I can't give you a definitive rule for all mags, but I believe you should rotate your mags at least once a month if you are going to let them sit loaded.
If you choose to let them sit longer, they'll still work, but you may lose reliability and you may get occasional jams like failures to feed. It's not a big deal on the range. However, if this is a self defense gun, it's not something you want to experience.