2 months after the test. Exact dates will vary and be published on the main jlpt website for each session.
JLPT certification can help academically at any level, as it shows some level of proficiency and seriousness. It can help as an employment qualification in the case that you want to work in a Japanese-speaking workplace, but in that case you want the N1. Allegedly there are jobs that will accept the N2, so you could take that first. It's also an advantage of course in any job that has any connection to Japan... even if it's not a formal requirement, it suggests you're more likely to understand something about Japan and the Japanese, and that you would likely be more successful if you ever had to interact directly with Japanese partners or clients.
I took the JLPT for personal accomplishment though. It is not very expensive to sit for the test, as such things go, unlike many professional or academic qualifications.