The important difference is that you can go back and read the text, but not the lecture. If you miss it, changes are it is gone. Better to take too many notes than too few. After all, you can easily strike notes that you find you don't need, but if you don't note something the first time around, you will probably not get another chance. Good notes contain not only the lecturer's main points, but supporting evidence and examples.
Full notes are important for several reasons.
From the perspective of cognitive psychology, main points alone may not be sufficient for understanding the material, and the long term goal should be understanding, not simple memorization. From a pragmatic standpoint, many instructors ask examination questions that not only require simple recall, but also application of concepts to specific examples. That is one way to test for understanding. Terms and definitions, figures and tables, and names are all important. Consider taking notes during films and class discussions.