Take an average panel with say 9000 holes and assume there are 6000 non 
functional pads. If it is a 4 layer with 1oz inner layers then you have nearly 3 
mil of copper extra for each hole with NFP's. This amounts to 18 inches of extra 
copper drilled during that drills life. Multiply that up for 6,8, and 10 layers, 
and then 2oz and even 3oz inners. Ground planes are the biggest culprit, as 
tracked layers generally have thinner 0.5oz copper which is not so bad.

There may be other reasons we manufacturers have for keeping them to overcome  
processing problems on particular designs, but we are talking about the majority 
of MLB's and not the exceptional cases. Let's keep them in during the design 
stage but let the manufacturer remove them or keep them depending on their 
judgement for particular designs or process.

Designers cannot object to them being left in and we do not want to persudae 
them that they should not be removed.
-- 
Paul Gould
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