Cockpit automation, if used with reason, has many advantages. It greatly reduces crew workload, as the automated systems take over routine tasks. However, if workload is reduced too much and the crew is left with nothing to do, it can easily happen that individual members become hypovigilant - which impairs situational awareness and crew communication. In order to minimise the risk of hypovigilance setting on, it is often recommended that computers should be regarded as additional crew members, implying that they are prone to error and require cross-check. It is paramount that the pilots create a mental picture of the current situation, think ahead and actively analyse what is going on, rather than simply sit in their seat watching what the aircraft is doing (passive monitoring).
"Disengage autopilot and fly manually." Incorrect. Most airliners do not encourage pilots to hand fly during cruise. The autopilot is used to decrease workload and increase passenger comfort.