If you are a racer, or an occasional jogger, having two pairs of running shoes will improve your running, while also extending the lifetime of your running shoes. Personally, I recommend rotating your shoes every day, for several reasons.
After completing a run, you need to rest, and take a break... so do your shoes! Especially after a long run with high humidity, rain, or abundant perspiration. Each of these conditions provide an opportunity for moisture to permeate the shoe, compromising the quality of the upper, and cushion areas of the shoe. While on this subject, let me remind you to allow your shoes to dry completely before running in them again.
Another good reason to let them rest, is the "foam-cushion" that protects your foot upon impact, is like a sponge. If you hammer the cells of this material without letting it "rebound", it will eventually compress, and remain compressed. When this happens, the tread on the sole of the shoe might still look pretty good, but the cushion is gone.
Sometimes I even change shoes during different phases of a daily workout. Selecting a shoe that is best suited for the run that I am doing. When doing a warm-up, long-slow-distance, or what I might call "junk miles", I wear a shoe that will be kind to my body upon impact. what I'm looking for here, is a shoe that cushions my impact like I'm running on grass, or wood-chip trails. The idea here, is to complete the run distance with the least amount of wear-and-tear on my body. During these workouts, I might be focused more on total miles, or total time of running. The down-side of the heavily cushioned shoe, is they can feel clunky, and have less snap, when coming off the ground for the next stride... so I rarely wear them in races
When speed is important, I wear a lighter shoe, that is quicker into the toe-off for the next stride. I call that "Eager For The Next Stride". You'll feel the difference with a shoe like this, because it is almost "begging you", to run faster. I typically save these shoes for special occasions, such as speed training, or racing.
Often times, I finish a workout in my racing shoes, after I have warmed-up with some miles in the cushioned, long-slow-distance shoes. The idea here is to get the body ready for running with the least amount of trauma. Then switching gears physically, and psychologically when I put on my racing shoes. There have been times that I've surprised myself with a workout, running 10 miles or more, followed by a faster tempo 3 to 5 miles. Sometimes my pace per mile during the faster segment, might rival my current race times for that distance.
Try some of these suggestions, you might enjoy your run more, and improve your performance too.