What's the purpose of the little pocket in the right front pocket of jeans?

From: Anitha @ Fidelity (Bangalore)

Watches! Back in the day before the wrist became multi-functional, folks carried pocket watches. These were fastened to the end of chains, and stored in special pockets woven into pants or vests. Levi's 501s, originally introduced in 1890, featured watch pockets. And sure enough, it was found that these vintage jeans from the 1970s listed as having "five pocket styling with watch pocket."