Bunglerat, what exactly does hand flying the jet achieve that the autopilot can’t when left hot and high? Can your arms extract a little more speed brake deflection than George can?
Zapatas, if you're a jet driver and you need to even ask such a question, the answer would probably be lost on you. If you don't fly jets, I'll give you the benefit of the doubt. Nevertheless, without the benefit of simple diagrams and pictures, let me give you an answer to the best of my ability...
Modern jets utilise multiple levels of automation, and a desired outcome can be achieved using more than just one mode available to the pilot. For example (and apologies for stating the obvious to the professionals who may be reading this), a descent on autopilot can be initiated using one of a number of options available for Boeing types - VNAV Path, VNAV Speed, Level Change, or Vertical Speed. Then there's Control Wheel Steering (another mode option again, but I digress). In the case of Airbus types - Managed Descent, Open Descent, Vertical Speed, or Flight Path Angle. Each mode is capable of achieving the same outcome (i.e. descending the aeroplane), but they do so in different ways - and the pilot needs to ascertain which mode is best suited to the situation at hand. In the case of the Boeing, VNAV Path (as the title suggests) places an emphasis on maintaining a descent
path rather than speed. If, for example, the aeroplane is descending with a strong tailwind and starting to get too high on its descent profile, VNAV Path commands the nose to pitch further down in order to regain the profile. Seeing as there is no speed protection in this mode, the result can be an overspeed if the pilot does not intervene with manual control inputs or switch to a different mode. I could cite various examples of the idiosyncrasies of every mode available, but frankly I can't be bothered. In short, the pilot needs to be aware that each mode has strengths and limitations for a given situation.
So back to your question: What does hand-flying achieve that an autopilot can't? Let me put it this way: When you run down a flight of stairs, does your brain process every muscle movement and count each individual stair and where to place your feet on them? No. If you were to consciously think about each and every step and where you were placing your feet, you would trip over in a matter of seconds. Such a task is achievable only because we are able to quickly and naturally perform such a task without consciously processing each aspect of it. The same is true in the cockpit. In the example I gave in my earlier post, if I find myself hot and high on descent with track shortening thrown in for good measure, I can do it all on automatics - but then I have to consciously think about every aspect of the process, which mode to use, whether it is best suited to the task at hand, and subsequently perform numerous keystrokes on the FMC or button pressing on the Mode Control Panel (glareshield) to achieve the desired outcome. In the process I'm having to work harder, because whatever my desired intentions may be for the aeroplane to do next, there is the issue of it taking just that little bit longer to achieve - because I'm directing a third party (i.e. the autopilot) to do it all. On the other hand, when I disconnect and hand-fly, there's nothing more immediate, direct, and fluid in execution than one hand on the control column and the other on the thrust levers.
I hope that answers your question. And in spite of what I've just said, I am still very much in favour of using automatics - but under the appropriate circumstances, as has only been reinforced by others on this thread. And in answer to your other question: I currently fly 737's, but am also A330 type-rated.