Why do people measure the value of all the goods produced domestically during a year?
From Wikipedia: "GDP was first developed by Simon Kuznets for a US Congress report in 1934. ... After the Bretton Woods conference in 1944, GDP became the main tool for measuring a country's economy."
Yes, the GDP number is, of course, imprecise. By itself it's not a problem -- most of our measurements are imprecise.
I am not sure what are you getting at. Do you think that GDP is useless or cannot be measured or what?
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.