A question about ironing. If I print a part that has a critical dimension and I ask it to iron the top surface, will that add to the overall dimension or will the software take that into account?
Good question. one I have never seen discussed.
Perhaps you could print two small test cubes, iron only one and compare?
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I did perform such a test and if anything, it actually increased dimensional accuracy in the z-axis. Remember all ironing does is move the hot tip back and forth to smooth out the extrusion lines without extruding any more filament. So as a result, there is no "adding’ of material but as the topic goes, the ridges are “ironed-out”.
From https://wiki.bambulab.com/en/software/bambu-studio/parameter/ironing, the they z-height is not raised as the print head moves over the surface again, but a small filament is usually extruded based on the flow rate.
So how I read this, it shouldn’t add any height, just add push a bit more filament into the gaps much like when using spackle to fill in nail holes in drywall before painting.
I am interested to see what your find from your testing.
I know I’ve used ironing a bunch to help counter that ringing issue BS seems to cause on models that have curved top surfaces, such as that of the shoulder of the Brick Hulk model.
Thank you all for the answers. I did wonder as it indicates that it uses a little more filament, but filling up the ridges would explain that 
Thank you all again
Mike