The Dart runs better than ever

Drilling the throttle plates is to get more air in the engine at idle whithout opening the throttle blades too far and uncovering the idle slots when very large camshafts are used. Once you open the blades so far and uncover the transfer slots you aren't running on the idle circuit anymore, you are running on the main circuit.

It's a valid technique when used properly. If you have less than approx. 265* of duration @ .050 lift though then it's usually not necessary. You can crack the secondary side open to gain the air flow. Ideally you want no more than .040 of throttle blade opening measured with a wire gauge. If your engine won't idle on that and everything else is right, then drilling the blades is valid. But it should be a last resort.