The things that come to mine are higher EGTs, lower NOx emissions, less power, potentially higher water and oil temps, and much, much faster turbo spool.
I've found it's usually better to have the octane and timing curves right and not use the knock sensor at all. Besides the fact that knock is bad, it will usually pull more timing to stop the knock than if you had the timing right in the first place.
As for the comment about the Honda Accord, they suck. My TL pulls timing all the time whether it's light driving or WOT. WOT shows over 10 degrees of retard. It takes a minimum of 96 octane to suppress the knock and my car is stock. Many others have this problem. I'm not happy having to run good gas in a 258hp car. The knock sensor should be a failsafe, not a normal part of the ignition system like Honda seems to think.