Gennaro Zezza, student and co-author of the late Wynne Godley and currently responsible for the Levy Institute macroeconomic model, gave an interesting talk on the usefulness of Stock-Flow with Consistent Accounting (SFCA) approach to macroeconomic modeling. He refers to the models as stock-flow consistent (SFC), but I prefer to emphasize that the consistency is not just about the relation between stocks and flows, but also the fact that these models provide the full set of accounts (website for those interested in this approach here).
SFCA proved to be considerably more successful than conventional, in particular Dynamic Stochastic General Equilibrium (DSGE) models, in predicting the Great Recession (see here paper by Dirk Bezemer).
As noted by Gennaro, the fundamental principle of SFCA models is that:
"in the economy – and therefore in models representing the economy - everything comes from somewhere and goes somewhere else: 'there are no black holes.' This obvious principle has relevant implications: one is that the debt of somebody is a credit for somebody else."
Note that this fundamental principle has more to do with the fully consistent accounting part of the model, than with the relation of stocks and flows. But stock-flow relations are also essential, since flow decisions of spending are tied to stocks. Private agents can spend if they have access to stocks of credit, of accumulated assets, that is, some stock of wealth. The State often has the power to spend and accumulate a stock of debt, since it can decide (Functional Finance and Chartalist approaches, which are implicit in Godley's work, become important here) the token in which debts are denominated.
One of the questions raised in the presentation was about the supposed lack of behavioral assumptions and expectations in the SFCA (as compared with DSGE models). First, it should be forcefully noted that there are behavioral assumptions, and those are strictly speaking based on Post-Keynesian (classical-Keynesian, I would say) principles. So agents autonomous decisions to spend create income, and in the models, I would add, investment follows an accelerator, so it tends to be derived demand, with the stock of capital adjusting to the flow of income (a relatively stable stock-flow relation, associated to the normal degree of capacity utilization).*
While DSGE models presume that an exogenous potential product (determined by supply side factors in a Ramsey/Solow/Lucas/Romer tradition) drives the economy, and deviations from it are corrected by price and wage flexibility, these models have an endogenous demand-driven output trend, which is really why they do better explaining the real world, including the Great Recession.
On the question of expectations Gennaro was clear, as a Post-Keynesian (PK) he is not particularly interested in expectations. He, however, suggested the possibility of using what Tom Palley refers to as model consistent expectations. That is, agents use expectations that are consistent with model (in this case the PK model, and, hence Lucas's problem is not that agents use all the available information, but that he has the incorrect model). Mind you the introduction of this expectational framework does little to improve the ability of the modeler to understand reality.
Finally, I want to note that while I do think that it is essential that these models, which are an alternative to applied DSGE models used around the world in Central Banks, international organizations, think tanks, and other institutions that managed to miss every single sign of the crisis, are developed and used more by economists, they should not be seen as the only modeling strategy available to heterodox economists.
In my view, the stock-flow and the demand driven (and I should say, the fact that price dynamics is orthogonal to the income flow determination structure)** is the essential characteristic of this approach. But the empirical, macroeconometric models that Gennaro and Wynne build have, more importantly, the full set of accounts, something that is essential for the empirical models, but sometimes too cumbersome for making a theoretical point. Hence, sometimes models that present the stock-flow dynamics (in a classical Keynesian perspective), without the full accounts (see here, for example), are necessary, useful and more directly relevant for the task of providing theoretical insight into a specific problem.
* This means that these are supermultiplier models in the Kaldorian tradition, which should not be a surprise since Wynne was a disciple of Kaldor. In fact, Kaldor was responsible to bringing Wynne to head the Department of Applied Economics at Cambridge in the late 1960s.
** Wynne was a student in Oxford of Andrews, one of the main authors of the Full Cost Pricing School.