We are told to wait for a few seconds to restart the router, but why?

Waiting a few seconds before restarting a router allows it to properly shut down and clear its memory. When you power off a router, residual electrical charge in its circuits, particularly in capacitors, needs time to dissipate. This brief pause—typically 10-30 seconds—ensures the router’s volatile memory (RAM) is fully cleared, resetting temporary settings, cached data, and any software glitches. It also allows network connections to terminate gracefully, preventing issues like IP conflicts or incomplete data transmissions when the router restarts. Without this wait, the router might not fully reset, potentially carrying over errors or corrupted data, which could lead to persistent connectivity issues.