It is a common business model among the high-paid. You have a sub-S corp, rent yourself out to companies and invoice them, and they pay out all the money to yourself as a salary from your sub-S corporation. This allows you to dodge the 2% limitation of business expenses, and deduct your medical insurance as a business expense.
I go out to lunch with a guy like this. We discuss business for five minutes, and then he writes off 50% of the cost of the lunch as a business expense.
Makes no sense to me.
If I invoice said company, there is no reason for them to do any W-9 withholdings. They would rather not be bothered by those paperwork requirements. I could be a Sales guy or a cleaning person and they would be much more inclined to just write a check and call it an expense.
As a Self-Employed person I get the gross amount and can manage my own deductions to off set my tax burden.