There should be reference plane (for +5V track it should be GND_M polygon on layer 2) adjacent to all signal and power connections. Typically it's a ground polygon or plane on an adjacent layer. Otherwise electromagnetic fields will spread out more and cause more noise. In a typical 4-layer stackup the layer pair 1 - 2 and 3 - 4 have small distance between them. When using one layer of a pair for reference layer and other for signal and power, the fields are more contained and less spread out, which helps with the noise.
ReikoR
commented
1 year ago 
There should be reference plane (for +5V track it should be GND_M polygon on layer 2) adjacent to all signal and power connections. Typically it's a ground polygon or plane on an adjacent layer. Otherwise electromagnetic fields will spread out more and cause more noise. In a typical 4-layer stackup the layer pair 1 - 2 and 3 - 4 have small distance between them. When using one layer of a pair for reference layer and other for signal and power, the fields are more contained and less spread out, which helps with the noise.