Multiple ground planes connected strangely?

[gmc]

I"m busy looking at a SMPS from a old IBM computer and have a query on why they have done strange things with the ground plane. If you look at the attachment the red dot is connected to  chassis earth.

Folowing the PCB layout the 2 blue dots are also earth. Why did they not just join them together via the shortest path?

I've also attached the top layout which shows some of the components.

Is there some specific reason for this odd layout? Extra resistance maybe?

[thm_w]

Usually its done on a voltage rail to have a current path pass through the area with filtering capacitance, to avoid noise exiting the area bypassing the filter.
In this case I doubt it would make much difference, usually you are better with a flood fill and not trying to be fancy.

https://incompliancemag.com/article/slots-in-gnd-planes/
https://learnemc.com/not-so-good-emc-design-guidelines

[gmc]

Thanks, that's a interesting read.