  The question of which and how a particular class of entangled resource states
(known as graph states) can be used for measurement based quantum computation
(MBQC) recently gave rise to the notion of Flow and its generalisation gFlow.
That is a causal structure for measurements guaranteeing deterministic
computation. Furthermore, gFlow has proven itself to be a powerful tool in
studying the difference between the measurement-based and circuit models for
quantum computing, as well as analysing cryptographic protocols. On the other
hand, entanglement is known to play a crucial role in MBQC. In this paper we
first show how gFlow can be used to directly give a bound on the classical
simulation of an MBQC. Our method offers an interpretation of the gFlow as
showing how information flows through a computation, giving rise to an
information light cone. We then establish a link between entanglement and the
existence of gFlow for a graph state. We show that the gFlow can be used to
bound the entanglement width and what we call the \emph{structural
entanglement} of a graph state. In turn this gives another method relating the
gFlow to bounds on how efficiently a computation can be simulated classically.
These two methods of getting bounds on the difficulty of classical simulation
are different and complementary and several known results follow. In particular
known relations between the MBQC and the circuit model allow these results to
be translated across models.
