I haven't done this myself, but for a defensive handgun it makes a lot of sense. If you're involved in a shooting with it, it will most likely get taken from you as evidence, anywhere from a few months to a few years. This isn't a good time to have to go unarmed. So it would be very convenient to have a replacement whose operation you're already familiar with and already fits your existing carry gear. But, for just collecting and shooting as a sport/hobby, I wouldn't get multiples of identical guns.