The reasons I rotate my tires on a regular basis, are already explained in the Tire Rack link that was shared above. First, after many sets of tires in my lifetime, I have found that a set of tires lasts much longer when I have them rotated on a regular basis. My practice has been to take my cars in for tire rotation shortly after each oil change. That works out to be about every 6,500 to 7,500 miles, depending on the car.
The second, and really important reason, is that most tire manufacturers will not honor tread wear warranties if you don't rotate tires regularly. This has paid off big time for me in the past. Pirelli paid almost 1/2 the price of my last set of Michelin tires, because of tread wear warranty. I wouldn't have gotten a dime if the tires had not been rotated regularly. I have been told by tire installers, that tire companies such as Pirelli, who's tires rarely make the claimed tread wear, depend upon owners who don't rotate regularly, and don't make warranty claims.
Comments about the expense of having tires rotated are foreign to me. If you are paying to have your tires rotated, you have bought them at the wrong tire store. I have never paid to have my tires rotated. In fact Discount Tire rotates the tires on my '13 Subaru Outback for free, even though it still has the factory tires on it. My Subaru dealership occasionally sends me coupons for free tire rotation, as does the local Big O tire store, a Western tire store chain. Why would anyone pay to have tires rotated? And why would anyone pass on rotating tires because they are too busy to do it themselves, unless they are one of those who don't like others to perform maintenance on their car?