[cortesoft]

Every tax will do two things: raise revenue and modify behavior. Usually, the purpose of the tax is the former, but you need to remember that the latter will still happen.

In the case of income tax, you raise revenue but you change behavior in a negative way (discouraging work). If you instead tax vices and consumption, you can raise money while not causing negative behavior changes (and maybe instead causing good behavior changes).

However, as the parent comment pointed out, you have to really look deeply at a tax to figure out how it will affect behavior. It won't always be in the desired way.