The preceptor system focuses on a two-way transfer of knowledge between the preceptor and the student. Preceptors benefit as students give feedback about the learning process. When the preceptor is someone long removed from the classroom, students can share their knowledge of the latest technology and classroom topics. Preceptors can provide students with feedback about their daily progress and share the wealth of knowledge they've learned during their previous experiences.
A preceptor adds another perspective on how to solve problems. She might have learned things differently at her university and might approach problems in a different way than how the student or teacher does.
A preceptor helps students in ways the students otherwise wouldn't get because the classroom teacher might not have time to deal with all the individual student's daily problems. In fields such as nursing, the students provide a valuable service to the hospital when they take care of patients. A preceptor relieves a classroom teacher from the additional supervising and teaching that would otherwise need to be provided without a preceptor.
A preceptor often works as a recruiter for the students to come work at her company. A preceptor and student can build a bond that leads to the two combining to work on research projects. A student might eventually show interest in becoming a preceptor herself.