Seeking precision in drawing geometric fonts would be easier while adjusting to lower number of Grid Subdivisions. But this might limit several operations which if you do not pay attention to nuances, you may end up with distortions and blemishes.
It is expressed in moving handles; transformations and importing from external files.
example:
Working on 2048 UpEm with a Grid spacing of 32 and 2 subdivisions while most of my font is build up with a consistent segment width of 160.
Started with importing from illustrator a square of 160 pt for testing into glyphs …the result came OK=160 (without any scaling) !!
But after importing a letter “E” where all three horizontal lines have the same 160 pt thickness; the result was after many pasting attempts into Glyphs: 160/160/176 !!
So I abandoned Illustrator and turned to do it in Glyphsapp.
A quick testing for a simple rectangle rotation results with minor distortion of which the rectangle corners snapped to the Grid and caused un-parallel distorted shape. {in cases with higher number of Grid subdivisions most of us do not notice such distortions}
Following up the previous discussions concerning Grid; I supposed GlyphsApp should have a quick menu switching of activating/deactivating “Snap to Grid” instead of redefining Grid parameters every-while in Preferences.