I really would like to habe a "fine tune" feature on this software as Slic3r and Kissslicer already have:
This "inset surface" is mainly to tune parts accuracy (I know that 3d printing is not very accurate...) but e.g. when printing the planetary gear set from Kickstarter this feature is VERY usefull.
Basically there are 2 ways of wrong dimensions on the standard 3D ptinters
1.) all dimensions of the model are e.g. 1% too small/large: can be solved via tuning the "steps per unit" in the firmware or by G92 X... and G92 Y...
2.) all dimension of the model are e.g. 0,1mm too wide: The printer extrudes a bit more material as it should, so you can simply adjust the flow rate.
On my printer I overextrude just a bit to get a perfect watertight solid surface on top but as mentioned every part is slightly (0,1mm) too large on every dimension. My RepRap is so perfectly tuned that I can ensure a perfect part accuracy but I really need this feature as it gives you the possibility to slightly adjust dimensions.