The employer needs to know the complete address of the employee for a number of reasons. One is for payroll purposes. Setting up an account for a person requires him to provide his address. Another reason is that if something wrong happens, they would know where to locate him or his family. The company also needs an employees address so that they can be certain of his identity. And another reason would be for mailing of anything necessary purposes.
A template for an employee form could also contain a portion asking for the employees office extension number. This would probably be part of the form especially in big companies where an employee may be reached by another in a different branch office through phone. The social security number will be part of the template. It will provide the company everything it has to know about the employee. If he has an outstanding warrant of arrest from the police, if he is an outstanding debt, what responsibility he has, what violations he did, etc. Other possible parts of the employee form template are the date of hire of hire of the employee, whether he is on a part time schedule or a full time one, a section where he has to say whether he just graduated or not, his pay rate, etc.