Van,
Depends on how much you shoot your gun. A 200 rd range session can leave a lot of powder residue in the mag body. If you shoot combat style matches where your mags hit the ground a lot, they should be cleaned afterward. With my duty and carry mags I clean them twice a year. I usually find very little residue in them. I have never had a mag problem with a Glock.
Stay Safe,
Savage