Is It Legal to Pay a Higher Salary?

I don't really get it. I understand that you want to pay less taxes and still have stuff like an apartment tuition a car. But why is my boss happy? Because he pays the lower salary and it's cheaper. And if they do, do they get in as much trouble as the Trump organization? Or is this a case of like, we have to nail these people,. We have to find something to nail them about?