Most cars today are tuned to use regular low octane gas. But that doesn't mean there's no improvement with a higher octane. My wife's car would get 32 mpg on 87 octane but it would get 42mpg on 93 octane gas. And it was a 1987 Nissan with 70 horsepower.
Most cars with large engines (V/8 and up) run smoother with premium gas. If your car isn't running like it used to, a tank (or 2) full of premium will clean the system better than most additives.
If you don't feel any power or performance improvements after a tank full of high octane gas, then your car probably doesn't need it.