What are the main differences, advantages, and disadvantages of using a drive-by-wire versus drive-by-cable system?
I'm restricting my answer to electronic throttle control, as I think a question shouldn't ask about too many things. Please ask another question about brake by wire and a third about steer by wire if you want to know more about those.
The main advantages of electronic throttle control is the elimination of the idle air control valve, because with electronic throttle control, the main throttle valve can be controlled. All of the problems that a faulty idle air control valve can cause go away with electronic throttle control. Also, you gain better control of an automatic transmission car, because switching gears can be compensated for in the throttle control. Furthermore, cruise control (including dynamic radar cruise control) became just easier to implement. As a minor advantage, it's possible to take into account accessory loads like air conditioning compressor. Oh, and you can't have a hybrid electric car without electronic throttle control in practice, because the hybrid control of electric motors and gasoline engines requires electronic throttle control.
The main disadvantage is that you're trusting the throttle control on a very complex computer with perhaps over million lines of code. For example, the Toyota electronic throttle control system has had software problems leading to sudden unintended acceleration. Also, finding causes of failures requires expensive electronic tools to read diagnostic trouble codes. There's also a "limp home mode" to allow you to drive safely to home or to the nearest garage, without proper throttle control. It's rare to encounter limp home mode because most of the sensors are duplicated, but it can happen.
I've been driving a throttle-by-wire car for a few years now. I personally don't care for it. The throttle is "soft", meaning when you blip the throttle when downshifting it gets a very weak response. It's "soft" in a number of other situations, too, but the blipping the throttle thing is what reminds me every day how much I dislike TBW. All my previous cars have been throttle-by-cable, a direct, physical connection.
I don't care for the disconnected feeling. Fortunately, my car doesn't have "Eco" mode which further dampens throttle action/response. I could never put up with that level of interference.
There is also the element of ceding control of your vehicle that I don't care for, either. With the growth of controlling vehicles from apps (remote start/stop, etc) it seems primed for misuse. My Luddite membership package is coming next week.
I personally believe people should learn how to drive and focus on driving when they are doing so. It's not that hard. Relying on all the electronic crutches gives them more free time to text and take selfies.