No agreed standard
Every stakeholder has a different picture of what good looks like, so the exercises get chosen around opinions. Start with a success profile and the day has something to measure against.
The day doesn't predict
A center can run beautifully and still tell you nothing about who will perform. Exercise choice, scoring and standardization are what decide whether it predicts, and they are the parts most often left to habit.
Judgment without data
Panels form a view from a few hours of observation. Aptitude and behavioral assessment, completed on the day, give them something objective to weigh it against.
Notes, not evidence
A full day of observation ends up as a page of handwritten notes that nobody reads again. Reports built from the same criteria give hiring managers something they can act on and defend.
No feedback
Candidates give you a day and hear a yes or a no. A structured feedback session turns the same data into something useful for them, whichever way the decision went.