Like I just explained. Modern engines run at the limit of spark advance before you start to get knock. Sometimes they go over and the knock sensors allow the PCM to see that predetonation and pull timing to a safer level to prevent engine damage. It only takes a second of knock (predetonation, or old schoolers call it ping) to destroy the engine (chipped piston, bent rod, thrown bearing, etc). So without the knock sensors your PCM will not be able to compensate for knock (which happens to every engine at some point, no matter how good the tune is) and your engine is toast when it happens. As I said before, it would probably happen the first time you put your foot in it.
It has nothing to do with blueprinting or balancing, and everything to do with ignition timing advance and predetonation. If you're not familiar with these concepts I suggest you read up on them.
