<p>Brand new to Slic3r, I've been using Cura for a while, so not sure is happening.  I tried to load <a href="https://www.shapeways.com/product/YDCPJF8KV/knight" rel="nofollow noreferrer">this Knight model</a> into Slic3er (v1.2.9 running on OS X), and it's reporting "Manifold: auto-repaired (11430 errors)", and the model looks incomplete.  Hovering the model with the mouse shows more details:</p>

<p><a href="https://i.stack.imgur.com/hb2DY.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/hb2DY.png" alt="Slic3r Screenshot"></a></p>

<p>Preview mode shows supports holding up the head, so I don't think it's just a screen rendering issue.  But I loaded this same model into Cura earlier today, and it worked just fine; I've printed the resulting GCode.  So I believe the model is fine.  I wanted to print using Slic3r and compare the results. </p>

<p>Is this a known issue with certain types of models?  Not sure what to try next.</p>

Dimensional accuracy is not as important as dimensional uniformity. I can print with undersized (or oversized) filament, adjusting the flow appropriately, provided the filament has a consistent diameter. When creating filament in-house, without expensive equipment, it is difficult to maintain the same diameter throughout the entire extrusion. It is likely this extrusion diameter (when creating filament, rather than the output of the actual print head) to which Barafu is referring when he mentions his tolerances: +/- 0.05 mm
in diameter
. Which is reasonable.
The "miniature printing" comment likely refers to printing miniature models for tabletop gaming.
If the source filament becomes wider than expected, the output will have overflow, or more material than desired will be deposited, and this will certainly affect the quality of the piece.