While I believe the tire shop gives free rotation to get you in the habit of coming back to them every few months so they can sell you more, it can be important to rotate your tires.
It all depends on the wear of the tires
I have had sets of tires that wore extremely evenly and I only rotated them once. Other sets of tires I have had wore very unevenly and had to rotate them multiple times during the life of that set.
For the question of rotation arrangement:
- It depends on your car's manual
- It depends on your specific tires
As other people have said, some tires are unidirectional and if you put the tires on the other side of the car, you will have problems. Most of the recent cars I have driven tell you to rotate your tires front to back and NOT across the car. I believe many manufacturers are going to unidirectional tires.
The real value that comes from rotating your tires is that when the tires wear unevenly, rotating the tires spreads the wear out more evenly on each tire as well, as over the set.
On each tire -— some cars and/or driver's habits cause the front tires to wear more in certain places of the tire, moving the tires to the rear axle generally cause those worn places to not get used as hard and wear the other places on the tires. (i.e.- alot, a lot of FWD car's front tires wear a good bit on the corners since they are used for steering and power)
Over the set -— the tires on the powered axle tend to wear out faster since more force is exerted through them to the pavement. To maximize the life of the tires, you switch the tires on the powered axle to the non-powered axle so that those less-used tires (with more tread) are used to even the wear.
