Back in my nursing days, I worked for a staffing agency at one point. I got paid better than regular staff and the facilities had to pay enough to the agency to cover not just my wage but the profit the agency made. Normally it costs the facility twice what I got paid. No way does a facility save anything by using agency temps regardless of benefits to regular employees.
An employee working 40 hours also is receiving Benefits, which are costly. That 41st hour does not include Benefit pay, often or usually, more than half the wage rate. Work them at Time and a Half pay for 60 or 80 hours, and save money.
Hire a new employee and pay their Benefits. Hire a Temp at twice the price or more. Better yet make everyone a Manager, define them as ‘Exempt’ and work them the 80 hours while still only paying them for 40. That is what my old Company did for decades and is still doing.
No way does a facility save anything by using agency temps regardless of benefits to regular employees.
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That was my experience also, as the Treasurer for the board of the local health center.