How does outstaffing work?

What process in business does not require qualified employees? All companies require good specialists, but it is not always possible to have a large full-time staff. For this reason, many business representatives use the services of freelancers and outsource business processes to contractor companies.
Outstaffing is the hiring of a specialist working in a contractor company (outstaffer) to work on a project in a customer company. The specialist is part of the client's team along with other team members, his work is regulated by the management team. At the same time, the client pays the contractor for outstaffing services under the contract, and he, in turn, pays the salary to the specialist.
here is an example: https://peiko.space/service/it-outstaffing-company
An example of outstaffing: in a large company, due to business expansion, it is necessary to increase the staff. This need for new employees exceeds the personnel plan for the year. What to do? Use the outstaffing service. New employees are hired, they perform their duties in the company, working along with other employees, but in fact they belong to the staff of an outstaffing agency.