“Always be yourself,” except when you're managing a company's Facebook page.
As a business owner in the 21st century, you have to manage a handful of social media profiles for your company(unless you hire someone to do it, of course, in which case you might want to forward this memo to them), from Facebook to Twitter, LinkedIn or Pinterest and many many more. Almost always people who manage these company accounts have personal ones, too. How do you know when to post as yourself as opposed to your company?
It can be a thin line to walk. Brands these days see huge success from being funny on social media and interacting with followers. But sometimes being funny and relevant can push the envelope. There are a slew of examples where a brand faced backlash for going too far from something that would probably pass unquestioned on a personal profile.
When you're posting as a business, you're under a microscope constantly. Going outside of your business's POV—whether it's relevant or not, timely or not—is dangerous territory. Don't post anything political unless you work for as a politician. Don't post anything religious unless you work for a church. It's as simple as following rules like that(sort of, kind of, not really, not at all).
The truth is, there's no right answer for when to be yourself. At least not a metric one. It's often a gut-feeling you have to follow, erring on the side of caution. Do post that viral article about cats that will have your followers laughing and sharing. Don't post an op-ed about Obamacare(unless of course it fits your POV).
No business owner wants to see a decrease in their following; it's virtually like having customers walk out of your business right before your eyes. When it comes to posting, use your gut and use it well.