It's Not Just Planes and Passives
Planes can cause problems with passives, but it's not just planes. Uneven traces - a big one on one side and a little one on the other side - can cause just about as many problems too.
The scenario in the image on the right can do a lot of damage to manufacturerability and reliability.The problems get worse as the parts get smaller. You can end up with a cold solder joint on the right side or tombstoning. And cold solder joints are worse than cold oatmeal.
Planes can hurt, but what about Euclids?