In terms of file size, JSON and YAML can have different efficiencies depending on the specific data and the way it is structured. JSON tends to have more compact syntax and generally results in smaller file sizes compared to YAML. However, YAML allows for more human-readable and expressive data structures, which can sometimes result in larger file sizes. It is important to consider the specific use case and the trade-offs between file size and readability when choosing between the two formats.