"However, to be useful, state machines must be organized in a strict hierarchy. A well-chosen hierarchy removes irrelevant combinations of states.” - yes state

"However, to be useful, state machines must be organized in a strict hierarchy. A well-chosen hierarchy removes irrelevant combinations of states.” - yes state machines are awesome and I use them all the time when programming real time controllers for machinery/process automation and sequencing. The best thing for me is that telling the process engineers I want them to tell me their required functionality as a state table (which then is our common/overlapping language of interface) forces them to think about every state needed and to exhaustively and unambiguously consider every transition. But, as per the text I included at the beginning of this comment, the surprisingly most difficult thing is deciding appropriate system decomposition and hierarchy so you don't end up with the "state explosion" of many, many states when someone tries to cram everything into one state machine.