Autopilots are GREAT.
They never forget to turn at flight planned waypoints, they are able to calculate the precise amount of drift required, and fly a heading that will maintain a very accurate track, when used in conjunction with a Flight Management Computer System (FMC).
As a matter of fact, they'll do just about everything they're commanded to do - as long as the CORRECT commands are given to them.......AND their initial programming is correct.
Regardless of the previous 2, they'll do EVERYTHING - without thinking - that they're ordered to do.
And THEREIN lies the problem!
Because I have had, on several occasions, autopilots that are being fed info from an incorrect data base, and autopliots that UNQUESTIONINGLY fly INCORRECT inputs, because the "programmer" simply made a mistake. eg. wrong flight plan routing; wrong hold info.
All with a SERVICABLE a/p!
Humans can think, check...double check.. and update/re-assess their projected thinking.
If a computer reverts to "static mode"/standby - which is frequently the case - there is no continuous system updating that allows IMMEDIATE Danger avoidance procedures.
Rather, the computer will stay in its present state, assuming the chances of radical change are negligible.
In aviation, this can prove to be be a FATAL mistake!