I've been wondering a lot about grounding practices on PCB layouts. My first question about it deals with vias. I've noticed that on a simple 2 layer PCB with ground planes on both sides, there will typically be a few or several vias spaced out to connect them with minimal impedance between the two copper pours.
However, on an RF board the via placement looks much more deliberate and I'm wondering about the theory behind this. The vias connecting the ground planes often border the RF trace. See this differential coplanar waveguide example:
I also have a second question about grounding on PCBs. When is it appropriate to "isolate" ground planes from each other? And how does having the ground planes on one layer (let's say top) isolated from each other help when both of those ground planes are connected to the same ground plane on the bottom through vias. When we have these isolated ground planes, does the via placement differ from either of the above cases?
Note: I'm aware of the possible duplicate here but I'm not satisfied with the answers and think my question asks for more detail.
Thank you for the information.