If you are putting grandma around doing the shoping duties in heavy traffic then is a waste of money.
If your engine is in good condition you will be able to slightly increase the engine intial timing (before pinging starts) and will result in a little more (but noticable) performance.
If your engine is high compression then is a neccesity.
Try it, it won't hurt your engine.
Just don't use fuels blended with ethanol !