There are two tabs: General, and Shape view.
In the General tab you can specify the following:
|Automatically check model after boolean operation||If checked, after a boolean operation it will be checked if the Boundary representation (BRep) of the model is valid. This is internally done by the function CheckGeometry.|
|Automatically refine model after boolean operation||If checked, the model will be refined using the function RefineShape after a boolean operation.|
|Automatically refine model after sketch-based operation||If checked, the model will be refined using the function RefineShape after a sketch of an object has been changed.|
|Add name of base object||This option has currently no effect.|
In the Shape view tab you can specify the following:
|Maximum deviation depending on the model bounding box||Maximum linear deflection of the tesselated objects from their surface|
|Maximum angular deflection||Maximum angular deflection from one tesselated object section to the next section|
In order to display an object efficiently its surface is tesselated, i.e. it is displayed with some small deviations from it real surface. This applies not only to PartDesign models, but also to other objects in FreeCAD.
There is a lower limit for the tesselation of 0.01%. If you really want to spend the additional time you can reduce the lower limit even further by opening the menu Tools → Edit parameters... This opens the parameter editor where you navigate to BaseApp → Preferences → Mod → Part.
Right click on Mesh deviation choose in the context menu Change value. Set the value to the minimum tesselation of your choice. Please keep in mind that the value is in %, i.e. for a value of 0.005% you have to enter "0.00005". The smallest value possible is 1e-7. Note: In the preferences menu you will still see 0.01% even if you set a lower value.