Vantaggi
Companies supplies employees to other clients. That is service company, that they make profit out of employees pay.
Svantaggi
Since this is a service company there are zero Benefits. Since they make profit off of employee's pay they offer might be lot lower then what client pays them. Off course they have to pay SS Tax, Medicare Taxes etc all those need to transparent along with their profit to employees.
Pay may not be good, hardly negotiable.