To use an ecological analogy, it's about as meaningul as the gross biological productivity of an ecosystem, which in the vast majority of systems means the amou

To use an ecological analogy, it's about as meaningul as the gross biological productivity of an ecosystem, which in the vast majority of systems means the amount of carbon converted to biomass by plant photosynthesis. However this tells you very little about the health of the system - it could mean a river choked with invasive weeds and toxic algal blooms, or it could mean a river full of insects fed on by trout that local humans harvest regularly as a local source of protein. Additionally, some ecosystems (like deserts) have low gross productivity, but as deserts go, are healthy ecosystems that just support less life than tropical rainforests do. Hence, you just need a lot of other numbers besides GDP to make sense of how an economic system is doing overall. Proably about a dozen at least, but that's too many for simplistic propaganda and click-bait headline purposes.