If you ever happen to take a class on philosophy, especially an introductory class, then the professor will usually make a statement about the importance of philosophy. It is common for philosophers to emphasize the importance of philosophy by telling everyone that all fields of study began as philosophy. They say that philosophy was the first science, the first in investigation and rigor, and from it we get all things, such as physics, chemistry, psychology and biology. In other words it is the root of all other disciplines and the source of all modern understanding, at least that is what they will tell you, and they will use examples from history to demonstrate that the study of philosophy lead to the creation of all the other fields of study.
With this in mind the professor of philosophy will then stress the importance of studying philosophy, because "By studying philosophy one learns how to think and to order one's thoughts so that one can make a coherent argument and participate in all fields of study." On the contrary, I have observed that a study of philosophy will not teach someone how to think.
All a study of philosophy will do is allow someone to articulate better their own way of thinking, it will not change the way they think. Only useful fields of study will actually change the way someone things (and the converse is also true). I have found from personal experience that after a study of philosophy a person will leave with exactly the same manner of thinking, but they will be able to articulate it better. This means that if someone begins to study philosophy and they already have a correct way of thinking then they will come out of it able to express correct, rational and coherent thoughts. But is someone begins to study philosophy and they enter it with incorrect thoughts then they will leave with incorrect thoughts, and even worse they will be able to express those incorrect thoughts in a more sophisticated manner, thus perpetuating their vile thoughts and passing them on to others.
Because I had the opportunity to study both physics and philosophy (and for the most part not concurrently) I could see the difference between the two in how they affect both myself and others. As for myself, despite all the classes I took and the papers I wrote, and the books I read on philosophy I cannot honestly say that it changed the way I think one bit. But in my time studying physics I can see a definite growth in the way I think. Also when I talked to other people, those that went through four or more years of physics had a very definite change in the way they thought. If you put some freshmen physics majors in the same room as some seniors I could tell that the seniors had a fundamental difference in their world views and thought processes from the freshmen. The same was not true of philosophy. I could find no discernible difference in the thought processes and world views of first years from fourth years. The only difference is that the fourth years could articulate their mental mistakes with a greater vocabulary and elegance. In all their study they never bothered or were never challenged to change the way they think. They still persisted with the same philosophical errors of thought that plague so much of humanity. In short, they never learned a thing.