Signal Integrity and Noise
A schematic draws a wire as a line with no properties. That abstraction holds beautifully for DC and falls apart on the edges — the few nanoseconds after a driver switches, when the wire is not a connection but a component, with inductance, capacitance, a characteristic impedance and a finite speed. For most of the time your signal is idle and the abstraction is fine. For the small fraction of time when it is changing, the wire is the circuit.