It is impossible to make every signal in an electronic device have its own coaxial cable to connect driver to transmitter right now. But we still try to cram as much stuff as possible onto a small PCB and make it work at 100s and 1000s MHz. A consequence of that is to control all the coupling that occurs between signals and the outside world. Unfortunately, something like a via transition makes that really hard to do. Ideally, every signal via transition would be surrounded by as many vias as possible, all connected together to mimic the shield of a coaxial cable. But that is pretty unrealistic, so we usually add a couple of transition vias around the signal via. Some people only add one, and some even don’t add any. Well, how many shall we add? You can answer by experimenting different configurations of stitching vias, or stitching capacitors. Once you’ve determined what configuration works for your stackup and your signals, you’d better verify that it was done correctly, and that your board will be free from all the coupling that occurs from signals transitioning through vias.