In the United States, it seems the Birth Certificate was required for one thing originally.

To prove eligibility to receive a federal benefit!

http://cliotropic.org/blog/talks/und...0/#fnref-439-9

From the article: "US law had specified for over a decade that aircraft companies must only hire citizens, but the wartime boom made this requirement relevant for many more workers.3 Despite the importance of being able to prove one?s citizenship with a birth certificate, in the early 1940s, about 43 million Americans?nearly one-third of working-age population?had no such document."