It is a valid point that you should not develop your side projects on your current company's time/resources without their permission. That said, general self improvement (learning new skills, areas of expertise) is always protected, and developing better relationships with your peers is also always protected. Both of those things make you a more valuable employee (both to your current employer and to future employers). And applying those skills to 'fix' problems around the office is also always protected as you're clearly working in the interest of your employer.