As your finances allow, it’s a good idea to have more than one pair of shoes to run in. Different models will distribute the pounding of running a little differently, so the impact forces will be spread more evenly throughout your body. In theory, rotating shoes should also help individual pairs last longer—midsole materials will have more time to decompress between runs, and the uppers won’t disintegrate as readily if they’re allowed to fully dry between runs.
If you’re going to rotate shoes, stick with the same basic type, such as a lightweight trainer from each of three manufacturers. If you’re tied to one brand, they should have models that are related but different enough to result in a slightly different running experience. If you absolutely love one shoe from one manufacturer and it’s undeniably the shoe for you, have two or more pairs at various stages of wear. Even those slight differences will lead to different distribution of some impact forces.