(en) Using an expected utility approach the effect of "risk subdividing" on insurance demand is analyzed. The results indicate that when the total property at risk is scattered only on a small number of pieces (with independent risks), risk retention becomes very attractive relatively to market insurance with a positive loading.
Eeckhoudt, L., Bauwens, L., Briys, E., & Scarmure, P. (1991). The Law of Large (small) Numbers and the Demand for Insurance. Journal of Risk and Insurance, 58(3), 438-451. https://doi.org/10.2307/253401 (Original work published 1991)