There's also the effect of water absorption causing corrosion to metal parts, and promoting water absorption in certain plastic fuel tanks. The latter has resulted in a lawsuit with motorcycle manufacturer Ducati, where they agreed to replace the tanks that were swelling and in some cases, rupturing due to water absorption. This only happened in the US, after E-10 fuel became popular. Regular octane does not absorb water.
My Ducati's past warranty, so the tank replacement offer doesn't cover me, once my tank swells or ruptures, I'm hosed.