I consider a net “high speed” when the signal edge rate is fast enough and the trace long enough that that transmission line effects must by accounted for. e.g. a net that requires a controlled impedance trace along with possible source and end termination.
If I am turning on an LED or static IO, an “ugly” trace route doesn’t really matter too much. However, I deal with boards in with fine pitch (0.5mm) BGAs, high speed (300MHz to 3GHz) signals and high voltage (4kV). On these there are so many complex constraint corner conditions, it’s hard to see it auto-routed without spending as much time entering the constraints as it would to layout.
Way back when starting with Kicad I stated:
We have now great 3D support, much improved differential routing, and just got area-based DRC support. The KiCad (and add-on) Devs have come a long way.
My next wish:
- IPC-2581 output
- Guided Bus Routing support (like Altium)