When employment starts, so does the employer-employee relationship. This type of relationship is defined by the kind of contract the employee has in the company. It revolves around the things they talk about and disclose to each other before the start of the employment. And before such employment, it is necessary that the company has certain basic information about the employee. This is basically for accountability purposes and for the sake of having a complete and uniform record of all employees.
Another downside to using an employment agreement template is the potential for building inflexibility into your business. In particular, employment law changes may invalidate or make an existing agreement out of date. If you use the same job template for hundreds of employees and the law changes, you may need to go back and have them re-sign new contracts. This would not always benefit the company, though it is a small risk to take to get the significant legal protections afforded by even the simplest of contracts.