The probation period (30/60/90) days at the start of employment or new opportunities can be an effective way to allow both the company and the employee to test the waters and see how well things match up between all parties.
Framing the probation period appropriately to not make it “do this or be fired” scenario can be a delicate exercise in diplomacy. Someone asked me recently what I felt about their policy of telling people “if you don’t do well in 90 days, we aren’t keeping you.” I commented that their needs to be a more delicate approach, and that taking such a hardline stance might set people up with the expectation that they are being watched on every move.
The probation period should be a give and take exercise, where management can monitor, make recommendations, and adapt training if necessary. Likewise, it should be a time where the employee should feel comfortable to address concerns that may affect their continued employment.