Easy Road to Dimensional Accuracy?

I have been fighting some dimensional accuracy issues for quite a while.   There are is all kinds of advice out there as to how to go about doing it and I have only gotten about as far as to make sure that my printers are extruding the right amount of plastic!  Leaving that out as an explanation for parts that I print being out of whack by 2-4% in either direction!

Part of my challenge has been translating the advice from people that use other slicers into stuff that makes sense for Simplify3D which is what I am using.   So I asked for help on the user forum for Simplify3D.   Someone pointed me to an option called "Horizontal Size Compensation".  It takes a number of millimeters (+/-) as an input but frankly I was not sure how to use it...and assume that it would be better if I tried to calibrate things the "right way".

More fool me.  I finally decided to try it and found that it ... works?  Below are a sample of the results that I got on my first couple of tests:

 

The first test was for a spacer that will hold an 8mm nut.   As you can see the print without adjustments was too small.   The print with a -0.1mm compensation was perfect.  So I thought that I would try a bigger and more complex piece and printed a #3DBenchy with the same compensation not really knowing what to expect.  As you can see, I got the same kind of positive result.

Am I missing something?  It seems a little to easy.  This is a feature that has been in Simplify3D since I bought it a couple months ago (not just since the upgrade to 3.0) so I really should have tried it sooner.  If I had I might not even written my mean post about Simplify3D as that feature alone is worth the price of admission!

UPDATE

This setting is not the answer!  At least not for all cases.  I am finding that when I print a large-ish part in ABS, one that requires dimensional accuracy, there is some shrinkage that needs to be accounted for when the part is printed.  I have not measured this on the UM2 but on my D4S it is about 1%?!?!   I know that the printer is moving accurately as I have measured physical movement on the x-y dimensions but my parts are still too small.  I am finding myself doing a test print, measuring it, and then reprinting with an adjustment factor.