I don't like those agreements, but luckily I have an employer that was willing to rework the agreement with me to a way that favors both of us. We changed the wording to cover that which relates to actual work done for my employer, in effort to lessen the likelihood of them trying to claim something unrelated to their business. Our agreement explicitly assigns to me the ownership of the project I began before taking employment with them. Much better than the "we own you and your mind" approach.