The quality of fuel as gone down, that is a big reason. You want to get the carbon off the rings. The older motors were designed when fuel was better. So if you use today's fuel in those motors, they need a little assistance. Technically, the lower octane fuel will burn hotter.
Heat equals horsepower up to a point.
Running fuel that over detinates or predetinates will cause your motor to burn down. Basically to make the fuel burn cleaner. 87 might even work better. If the owner's manual says 87 is recommended, I'd use it. Use the minimum that is recommended.