For us economists and statisticians, the poverty threshold is an excellent tool that helps us figure out how different nations are doing economically and what their living standards are.
I work for an organization that researches poverty threshold among other things. We look at how different countries determine the threshold, the percentage of the population that is below the threshold and how this changes from year to year.
If a country is doing well, meaning developing it's economy, making money and reflecting these changes to the public by providing more jobs, higher incomes and more government services, people will slowly move from under the threshold to middle-class status. This helps us determine how their quality of life is improving (or not improving) as they develop. It also says a lot about a government's policies.