No, your source code is not a "crown jewel" or a "trade secret". Without people, infrastructure, environments, and keys, it's just a load of text files.
This is a myth propagated by engineers who overvalue their work.
Also, Google only has 1 REPO, which everyone in the company has access to. http://www.wired.com/2015/09/google-2-billion-lines-codeand-...
I love this response as well:
"Assuming you are using Git, that means every developer you employ is running around with a complete repository history of your source code on their laptop. They probably also have internal documents regarding design, product management, etc. Many of them probably use a cloud backup service like Mozy/Dropbox etc. I don't think Github is the weakest link in this chain. That aside, source code is typically far from your most valuable asset, especially if you're a SaaS offering like many startups. What could a competitor do with your code, absent your people and your branding? Even if it were, Github would probably be the least of your security concerns."
https://www.quora.com/Do-any-startups-use-GitHub-as-a-reposi...