There are three great reasons to train without ammo (dry fire). The first is that practicing pulling the trigger knowing there’s no bang gives you the opportunity to really focus in on what your arms and hands are doing. The second is that ammo is not as cheap as it once was. The third is that you can practice in your house for even as little as five minutes whenever you have some free time.
The purpose of training is to build up muscle memory. When it comes time to fire your gun, your body will instinctively behave the way you’ve been practicing without you having to think about it so you’ll want to make sure that what you’ve been practicing is correct.