Today I read in a non-scientific article that Amazon requires some physical workers to sign non-compete agreements. I used to think that the idea behind allowing non-compete clauses in contracts is to protect a companies' intellectual property. The article mentions that non-competes may also serve to protect a company's investment in case it pays for the employee's education or training. Neither of these seems to fit this case.
What scientific articles (in fields of mathematical economics, such as Industrial Organization) describe models where allowing for non-compete clauses improves the situation of both the employer and the employee?