The ‘worker’ employment status is a very flexible one. An employer cannot coerce the worker into accepting any they are offered, but neither are they obliged to offer the employment protections of a fully-regarded employee.
The ‘employee’ employment status offers more stability. The contract offers a security to the employer that the can rely on the employee in fulfilling their duties. But, they need to offer this in exchange for a more secure employment package for the employee.
The ‘self-employed’ employment status offers the employee the most freedom and flexibility, but they aren’t protected by any employment rights. They would be a great option for companies that require help on a single project.