Remuneration during the trial period

Here, in connection with finding a job, I wondered what goals the employer was paying for the reduced salary during the probation period? Save? This begs the question - why? And who needs a company that is trying to save money on an employee at the time of the device?

What goals does the company pursue in paying out a trial period of not 80 thousand, but 77? What is the catch?

And what goals does the company pursue, which during the trial period pays not 80 thousand and 40?
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Not a joke, I stumbled on this issue. The truth immediately realized for myself that I would not go to work for a company whose sn in the trial period is different from the main one. The probationary period is given to the employer and the employee (!) In order to take a closer look, so that you can leave without serious consequences if you do not agree on something. But I did not see the point in cutting the sn. Any ideas?