Just to be clear, a W9 form is a form that a contractor or employee gives TO a client or employer. The only reason an employer will give a w9 TO an employee is to make sure they have a blank one so that they can fill it out and return it.
By law, an employer must keep a completed, signed, W9 form in file for each employee that that they have. If they have a contractor who they will send a 1099 at the end of the year, they must have a signed W9 on file for that employee.
The purpose of the W9 is really just to have a sworn statement from the employee/contractor saying 'this is my SSN or Tax ID'.
So, if you are an individual, sole proprietor, or full time employee then you MUST complete and return a W9 to the person who's paying you, by law.
If you are a corporation/LLC then you are NOT obligated to provide a W9 and the employer/client is NOT obligated to send you a 1099. However, some companies will still want to to it. You can refuse, they can insist, you can decide how you want to handle it.
For me, I will of course sign/submit a W9 if I am working as an individual (which I don't do). For my company, our clients aren't required to do the w9/1099 thing so I refuse to do it when I'm asked.
The reason is that a vendor who requests that a corporation like mine do a w9 usually doesn't realize that it's not required by law, and people who don't understand taxes are more likely to make tax mistakes. I had such a client send a 1099 to the IRS with the wrong amounts on it, and that was a hassle for me.
Your interpretation of the word 'contractor' and the carpet cleaner analogy is incorrect. If you are providing a service and getting paid for it, you can be considered a contractor. The only provision I know of is that there's a threshold under which you don't have to file w9/1099, and I think it used to be about $600 but I'm not sure about that.
Basically, if you are required to file a W9 and you aren't planning on cheating on your taxes you should have no problem with it.