My car will run everything including E85. Yes the fuel economy goes way down but the break-even point math is pretty easy to figure out. When gas prices spiked years back around $4/gallon it was definitely a good deal.
Premium is good for the Harleys as others mentioned due to the typical elevated head temps when riding mid-summer.
Higher octane = slower burn, which also enables more timing advance.
On the same octane fuel, I get slightly better fuel economy on the 100% fuel vs 10% ethanol blend. The 10% ethanol is nice in the winter, though, as the ethanol scavenges water. No more frozen fuel lines (anyone remember adding Heet in the winter?)
While I do run regular unleaded in the car, due to the variable timing advance, if I do run premium the fuel economy and power noticeably increases.