Modern ECU, fuel injected motors will automatically adjust to burn lower grades of fuel. You just won't get the performance numbers advertised in their brochures. I know for a few model years; VW's had an octane sensor that would trip the CEL if you didn't fill certain model cars with premium fuel.
My Prius was set up to run on 87, my ZR1 was set up to run on 93 "minimum", but I run 104 when I really want to play. I don't need "anyone" to tell me what I need...or want.