Tullio Jappelli and Luigi Pistaferri have a recent paper called Fiscal Policy and MPC Heterogeneity. Here’s an interesting figure from it that shows how MPC varies by cash-on-hand:
So why does this matter? As Tullio Jappelli and Luigi Pistaferri put it:
the results have important implications for the evaluation of fiscal policy, and for predicting household responses to tax reforms and redistributive policies. In particular, we find that a debt-financed increase in transfers of 1 percent of national disposable income targeted to the bottom decile of the cash-on-hand distribution would increase aggregate consumption by 0.82 percent.