Hard stepping will make the flex a tad bit stiffer. You'll usually see a lower ball flight and could help with some numbers (spin, etc.) when fitting for the perfect irons. Example...I fitted a guy once for some 712 MB's. He was super consistent but his spin was a couple hundred RPM's too high, optimum launch angle roughly 1.5* too high...with the same iron, hard stepped, his numbers were perfect. 

Christopher,

Hard stepping shafts can help to lower the launch and spin when compared to standard shaft installation. 

Cameron

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Christopher, Hard Stepping or Soft Stepping is not routine but as pointed out is great for adjusting slight variances to lauch angles and spin rates...I have been doing it for years and find it a valuable tool!  It will make a difference albeit small for fine tuning!

1 foot of apex for every cpm change so hardstepping would lower apex by 1 yard