Well... there's "won't share" and then there's "don't share." The latter is easier to talk about, so let me cover that first. Of course there are things that I "don't share" at least as in "by default." That is to say, I don't (despite what some people might think) broadcast every thought that comes into my mind, and everything I know (or think I know), out to the world. And people probably appreciate
that.
At work though, I am pretty free with sharing knowledge and information. There are things I don't necessarily go out of my way to share, but I'm not sure there is anything at all that falls into the "won't share" category. That is to say, if specifically asked about something, or in order to accomplish a task in a collaborative setting, I don't know that there's anything that's such "secret sauce" that I'd try to keep it concealed.
By and large this approach has worked out for me over the years. I've never found much value in intentionally trying to be super secretive. Conversely I think I've benefited from being very open and quick to share knowledge, even if not in a direct, immediate, financial sense. But I think having that attitude (in some companies anyway) has a general effect of creating the perception of one being a good team player, a knowledgeable, helpful, and enthusiastic co-worker, and somebody that people like and want to work with. And that in turn helps "grease the wheels" in terms of getting people to cooperate with you, support your initiatives, give you good 360 review feedback, and other things that have real (albeit not immediate) benefits.