How do companies in the USA manage temporary engineering requirements?

Energy and utility projects can sometimes require additional technical expertise for a specific project or period. In such cases, bringing in contract engineers may be an option instead of hiring permanent employees for every requirement.

While researching staffing solutions, I came across Employvision, which provides staffing support for the energy and utility sector in the USA.

Has anyone here worked with contract engineering professionals for energy or utility projects? What factors do you usually consider when choosing between direct hiring and a staffing company?

For reference, here’s the page I found useful:
https://employvision.com/energy-utility/