What are the main features of a hybrid coding scheme?

In fact I don't what you mean by saying hybrid but I suggest that you talking about QAM coding method which depend on changing of the amplitude and phase of the signal to increase the data rate.

So the main features of hybird coding is support higer data rate for example

QAM can carry2 bits on each buad or sample.

16-QAM sample can carry4 bits.

64-QAM sample can carry8 bits and so on.