The problem with "unless it knocks" is you won't hear it knock when it is harmless because your engine has knock sensors that hear it before you do and signals the PCM to retard the timing to reduce it. When you do hear it, that means the PCM has done all it could to protect you and now damage is being done. The owners manual tells you that damage may not be covered under warranty. Why would you risk that?
It's telling you that premium is recommended and not required because what if you were out of gas and the station you pull into was out of premium(that happened to me once with my Turbo RX7). You can use regular to get somewhere to fill up with premium, but it should not be a practice. This engine was designed to run on premium fuel. Now, I would not put diesel or ethanol in it because that would cause it to stop, and cause damage, but regular fuel can, potentially, cause damage. Why would you risk that?
I don't under stand why anyone driving a performance vehicle, after paying "gas guzzler tax" of $1300.00 would even consider using regular gas in it that could possible damage the engine to save $3.60 - $4.00 per tank of gas.
I don't get it. Is that why you would risk that?