I got a Java certification at a large enterprise years and years ago. The only benefit I gained from it was that it forced me to systematically learn the language in greater detail than I would have otherwise. I personally found the experience valuable, and I think I have a higher level of skill with Java than many of my coworkers as a result, but no one is going to accept the certificate as proof of that.

tl;dr: Certification tests provide decent motivation to keep you trudging through hundreds of pages of technical documentation.