The aggregation of heterogeneous households and firms implicitly matters, together with liquidity constraints and various kinds of buffers and rigidities, in the "old-style" macro-econometric models that are still, by necessity I would say, widely used in generating our forecasting scenarios. Allowing more explicitly for these characteristics, these new models definitely contribute to improving our understanding of the ways in which monetary policy operates.
In traditional DSGE models, given the assumption of the representative agent, monetary policy affects the economy mainly through its direct impact on intertemporal substitution, in other words lowering interest rates increases aggregate demand by making consumption today more convenient than consumption tomorrow.