1099s report payments made to non-employee service providers, as well as payments to suppliers and other entities you do business with. Think of your own organization:
I9 is a form that employers MUST RECEIVE during the hiring process BEFORE THE EMPLOYEE STARTS WORKING. Employers take a high risk of not obtaining them prior to employment. The IRS and the USCIS both have specific rules on how to obtain, verify and process these forms.
The bigger the business you are, the more complex your compensation structure, and whether or not you use a third party, you should know about the details of this form.
From an employer's perspective, the rules can get complicated. Not withholding what we should has major consequences - as does deducting what we can't. If you have an organization of any size, you need to understand more than just federal and state tax withholding.
The bigger the business you are, the more complex your compensation structure, and whether or not you use a third party, you should know about the details of this form. It's difficulty makes it easy to make mistakes. Mistakes are easily caught by the IRS.