Its as if my mind is freed by committing to paper one set of observations and ideas to look for other nuances other patterns. Note taking becomes part of a disciplined observing and thinking in the field. The more you record and observe the more likely you are to potentially recognize anomalies, and the recognition of new patterns or anomalies is the crucial first step to new insight. I suggest you record not only what is directly important to and supportive of your research and ideas, but as time permits, observe what might be related, but is not understood. Anomalies will not be apparent if you look narrowly.
Writing is an important mode of exploration.
A final and most important reason to take detailed and extensive field notes is simply that others can benefit from your notes. In this way field notes are inherently different than a journal - a journal is a personal endeavor, field notes a public document. As Dr. Shroder pointed out, geologic field notes can end up under scrutiny in court. It is common to see in student's notes, the final interpretation and other lecture details given by the prof for a feature seen during the field trip, but not to see the observations and arguments that support or lead to that interpretation. In philosophy it can be hard to distinguish facts and observations from models and interpretations, but the former are more durable that the latter.