A specific person (not a team as in the case of agile squad), who has certain characteristics that are needed for the project, is hired.
It is the client who is in charge of assigning tasks and controlling the work of the hired person, while the company provider of the resource is responsible for their suitability and takes care of replacing them if necessary.
In order to be successful with this modality, it is necessary to plan an adequate onboarding of the new team member, to explain the working modality, the objectives to be fulfilled, the tasks to be carried out, the quality requirements, the team members, etc.
Unlike a squad, hired professionals cannot be changed from one iteration to another. That is, a specialist hired joins the client’s work team, either for a complete project or for tasks of several projects.
In short, staff augmentation is applicable when you already have a formed team and you need to fill a vacancy for a certain time.