What's the difference between gas grade?

Especially talking about the 85 and the 93 ( usability referred to as special and premium ) . Is there really a significant difference or have I been wasting my money on premium gas?

And for people who knows cars, I have a 2011 Honda Accord SE ( special edition) . Is buying premium gas even necessary for the car? Or would special be at better fit?

Thank you so much for your help in advance.

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