Open source development is the future of software.
It’s great for users like you and me because open
source software is usually free (not always) and
often safer to use because malicious code is less
likely to be implemented.
Gain Programming Experience
Build a Practical Resume
Using the Product
Promote Open Source Culture
Give Back to the Community
Referrence:http://www.makeuseof.com/tag/people-contribute-open-source-projects/