The “Kerf” is the width of a groove made by a cutting tool, e.g. the width of the gap left by the lasersaur laser when cutting, which is approximately 0.3 mm.
Here's how to take any inkscape drawing and compensate for the kerf, such that the resulting cut shape is closer to the intended dimensions.
Measure material thickness before drawing! If material is 5.6 mm and you draw assuming 6 mm, you still wont get tight fits.
Recommended: Ungroup and/or break apart into individual paths
Select all paths you want to modify (Ctrl+A)
Set Stroke Width to 0.3 mm (typical lasersaur kerf/cut width) (Ctrl+Shift+F > Stroke Style > Width)
Convert Stroke to Path (Path > Stroke to Path). This will create a narrow filled area where the path was.
Break apart the result (Path > Break Apart). This will separate the inner and outer path. They are now both completely filled areas.
To see them as two individual paths, set *Fill None*, *Stroke Solid Black*. You now have two paths for each shape.
Remove inner path or outer path depending on whether it's a shape or hole
The resulting line will be exactly 0.15 mm offset from the original line, so that the kerf (having 0.3 mm diameter) should cut right up to the original path.