primitive channel vs hierachical channel

Hi

As i know, there are primitive channel and hierachical channel in systemC.
But i'm not sure about should i know both of things?
If you can, could you please let me know what thing is used for normally in company.

Also second question is that can be possible use sc_signal and sc_fifo and sc_buffer in one module?
If yes, what am i caution for using that in one module?

Thanks