The frugal innovation approach takes place in developing countries to develop simple but essential products for low-income population. This approach asks for careful trade-offs to target a just-enough between cost reduction and essential value of the product. In this paper, we aim at understanding how the essential value of a product is defined during early design phases, and how it guides the " just-enough " between affordability and performance. Our study of five frugal products in India shows three strategies that define differently the essential values and their associated just-enough: design by aggregation, design by extension, and design by focalization. Design by focalization seems to answer frugal design issues, as it isolates the essential value in order to reduce drastically the overall cost. The introduction of the concept of Non-Trade-Offs (NTO), meaning the non-negotiable elements that guide design choices, helps understanding how to separate this essential value from additional functionalities. Our study gives new directions for both practionners and researchers towards a design for essential value, in developing countries but also in westerns countries.