VLANs provide security boundaries. You can later apply Access Control Lists (ACLs) between VLANs (using a router-on-a-stick or a Layer 3 switch). This isolates sensitive departments (e.g., Finance) from guest Wi-Fi networks.
Suddenly, PC2 (Engineering, S1) went dark. Not just isolated—gone. The port was still there, but the VLAN didn’t exist. The switch didn’t drop the packets; it just shrugged. 3.3.12 packet tracer - vlan configuration.pka