Somehow I got the impression it was about quite the opposite.

It said that your emotions control your thought process. It didn't say that was a good thing, it said it was a fact.

Emotions are powerful tools, and should not be undervalued.

Nor are they to be used inappropriately. Negative emotions in lasting doses are likely harmful to your health, as well as to your rationality. Depressed people aren't thinking rationally.