This is a particularly good question to ask (along with why) when youre writing.
Write a blog post ask yourself, So what? And see what you do with the words. They focus the mind.
Spend a day working for others, ask So what? and see how you feel. Did you make the world a better place? So what are you going to do about that?
I now kill more blog posts than I publish because I ask, So what? when it comes to this space. And I shake my head at myself recognizing my venting as essentially useless drivel that makes me feel good yet doesnt add anything.
So what? Its a useful question against which any project can be measured.
And by the way, the first trick is in not being paralyzed by it but in bulldozing your way through. Sometimes though writing doesnt need a so what? answer and the second trick is in recognizing the difference.