The quote from his Hakdama actually says that it is for
Halacha Lemaase. The issue is about using the dry Halacha, without knowing any background, to decide on a case that comes up. The issue is not about following the Halacha as written.
The Beis Yosef in Hlichos Tzitzis quotes an Achron who made a mistake before he looked up the source quoted by the Tur, and changed everything when he saw the Mekor. The Beis Yosef says that he brings the whole piece to show how important it is to follow the source to its origin.