Because fieldwork depends on the researcher as instrument, developing a sense of self is important for a variety of reasons. First, understanding the unchangeable attributes one brings to fieldwork is useful–things like the impact of gender, race, ethnicity, and religious beliefs. Second, monitoring your reaction to places, people and interactions may be key to identifying both over and under sampling within the research context. Third, using your own feelings, thoughts, reactions may be a pathway to developing an empathetic stance in the research context.
I have found Alan Peshkin’s notion of subjective “I”s useful. Take a look at In Search of Subjectivity.