Corporate personhood means that you can own a piece of a company without being personally liable, because the corporation is its own legal entity. This is why people can start businesses without worrying about being in debt for the rest of their lives if it fails. After all, if the corporation isn't a separate legal entity but just a collection of investors, if the corporation wronged someone, the investors could be sued personally.

Maybe the concept is taken too far in terms of political donations and free speech but no corporate personhood would mean that very few people would stick out their necks to start or invest in companies. I don't think a modern economy would even be possible.