While not mandatory for developing better shooting skills, having an extra set of magazines will make your shooting sessions a lot easier. Let's face it, unloading magazines every time you want to practice and then reloading is annoying and not the best thing for your ammunition. By owning an extra set of magazines, you can have one set for carry and another for practice.

Besides convenience, alternating your magazines will improve their reliability as the springs will not fatigue as quickly. Remember that you don't have to completely unload a magazine to save the springs, its typically the last few rounds that really stress the spring. I keep my extra magazines loaded with five dummy rounds each. This means that when I practice, I have magazines ready to go and the magazines are still enjoying the benefits of not being fully loaded.