Getting back on topic - how I feel about sharing information. Well I am an open person, and that sometimes hurts me, because of the willingness and excitement to share, I may sometimes share a bit too much. Yes, sharing certain information can be harmful more than do any good. Or it may do good for a period of time until it spreads.
If I have something cool, be it my own creation or something I found, that no one else has, but there's no direct or good benefit for myself, I am willing to share with anyone. However, based on the importance of it, I may decide to share it with certain people, or a certain group of people (usually it's the VIP section).
Most of the projects I make, are all opensource or otherwise free (unless it's a project I was paid for), because there's no benefit for me to lock it down. But eventually I might share the project anyway...
Now why am I doing it - is simple. I feel good about it. I have my own blog where I publish it all first, there when I write and share, I get no direct benefit at all, my blog isn't a popular place, I probably get one or two lonely readers per day, but I don't care about it, because it's for people that are searching. It also acts as a reference for myself in the future, I learn to write fluently, I deepen my knowledge by writing. And ofcourse that's how you create a portfolio.
IMO, when sharing something, you need to evaluate if it's worth it. Obviously if it's like "hey people look at this really cool search engine I found:
http://google.com" then it's useless and sharing it is stupid.