An open seat costs throughput. A placement that fails at month four costs throughput plus everything you already spent: recruiting effort, onboarding time, training, supervisory attention, the disruption to the crew. Then you still have the original open seat, and less time than before.
There is a cost you never see as well. A technician whose first placement went badly often decides the industry was the problem rather than the match. You lose a hire. The trade loses a technician. With the Bureau of Labor Statistics projecting roughly 13,100 openings a year through 2035, that is a loss the sector cannot absorb repeatedly.