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In terms of radio waves, besides intended emissions like WiFi, well designed modern circuits release little spurious electromagnetic radiation. There's a whole field of engineering that goes into this, called electromagnetic compatibility. Basically the layout of the board feature ground planes and return vias that improve signal integrity while reducing any unwanted emissions.

Avoiding interference is not just altruistic due to the reciprocal property of electromagnetism: a design that does not accidentally create antennas and emit junk, is less susceptible to receiving interference from external sources