"This means their productivity suffers at their full-time job, an expense the employer ends up paying."
Incorrect. My side projects have made me a better developer in every way, which actually saves my employers money over the long-term. I learn new techniques, skills, and tools off-the-clock. The kind of training that used to be the responsibility of the employer is now on the employee.
Agreed. I had a side project that ended up driving adoption of several applications that had components from the project that saved the company over $100k per year in employee costs by automating things that were previously very manual.
This one goes both ways. Yes, your employer will benefit from what you learn from your side project, but at the same time, if your side project's server crashes at 2pm while you're at work, you're going to be very inclined to fix it right then and there on your employer's dime.
Incorrect. My side projects have made me a better developer in every way, which actually saves my employers money over the long-term. I learn new techniques, skills, and tools off-the-clock. The kind of training that used to be the responsibility of the employer is now on the employee.