Although there is no law that requires employers to have employee handbooks or personnel manuals, they are one of the best tools for communicating information to employees about your company's policies, their performance standards, and employment benefits. By having written policies in place, an employer is also able to develop uniform standards within the workplace that can help promote fairness and the consistent treatment of its employees. Handbooks are therefore a must in terms of an employer's ability to comply with their legal obligations to their employees.
An employer that does not have written guidelines in place is much more likely to encounter problems arising from ignorance of its policies, inconsistent or unfair application of those policies, conflicting policies, and resulting confusion among its employees. This can lead to internal problems such as employee dissatisfaction and discrimination charges filed by employees who feel they have been treated unfairly.
Jacqueline McManus has an excellent article in the Monterey Herald describing all of the reasons why an employee handbook is really a necessity for even relatively small employers. I reccomend it to you for your consideration.