Thanks Jensen & Bugbyte,
But I think zapro is merely kidding,
If not, he risks losing credibility...
It's primarily an olskool rule to do with under etching as I said. And thermal/mechanical stuff - but with square SMD corners and 90° corners where track meet pads etc.... (Need I go further?)
If you're into waveguides - fine, there is an issue. Or if those tracks are handling signals above several Gbs - but 90° bends may then be an advantage (ie, lower capacitance/impedance).
Otherwise the signaling issue is out - that is more dependent on surrounding tracks.
Maybe zapro is playing with my relations across the Sound Strait.... Those Nordics are schemers eh - aren't they Jensen?
(Or was it that I linked electricity with magnetism? That'd make me as smart as Maxwell, smart eh?)
For those that are concerned, a quick google should find a few good research papers or their webbed summaries.