Cells face various allocation problems demanding decisions on how to distribute their finite resources. Much of their biomass and energy is invested in the production of enzymes, which in turn catalyze and control most of their biochemistry. Cells not only decide which enzymes to produce when and at what quantity, but also where to position them. I will focus on this latter, spatial allocation problem of arranging enzymes such as to maximize the total reaction flux produced by them in a system with given geometry and boundary conditions. Due to the interplay of stochastic transport with local, enzyme-catalyzed reactions, this optimization problem naturally leads to a bet-hedging strategy on the molecule level. The optimal arrangement of the enzymes is deeply connected to the statistics of the substrate molecules that react on the enzymes. I will describe an optimal spatial allocation principle that is analogous to a portfolio optimization of investments that globally feed back onto all payoffs. This principle allows us to understand a localization-delocalization transition in the optimal enzyme distribution, reveals the generality of the transition, and produces a practical test for the optimality of enzyme clustering. The underlying criterion also serves as a design principle for synthetic biomolecular systems.