@dang, madengr's insightful comment (sibling of this) seems to have been unfairly murdered? He's absolutely right.

For EM analysis, it actually helps to be “on grid” as the gridded solvers have a lot more dynamic range than gridless, like 100 dB more. Analyzing structures such as filters require high dynamic range, so adding a bunch of curved artwork will introduce errors in the simulation, or take much more resources. I do all my PCB layouts on a 0.1 mm grid and try to keep things snapped. I’ll even round footprints to the nearest 25 um or larger.

Also, the GDSII format for IC does not handle curves well. Unlike DXF, it can’t handle a circle, so has to decimate it into a polygon.

When doing signal integrity analysis on PCB, the tools can break those long runs of straight, parallel lines into closed form models (i.e. coupled transmission lines) which greatly speeds up the analysis. With a bunch of curves, you can’t do that, and it has to break those out for EM analysis.

If one could easily make square via holes in PCB, those would be preferable for situations like grounding vias as they better terminate the EM wave.