Ethics of using previous work for a new assignment

Do you feel pulling information from previous personal writings is a means of limiting you as an individual and/or student.  As you are not writing material from freshly researched material that provides you the ability to gain new insight/knowledge on the subject matter?  Or do you feel it is a way to showcase the knowledge you have gained and put it in a new perspective.  Allow the individual to build upon their previously learned material with fresh new ideas and research?  Allow you the opportunity to begin mastering the information through previous teachings and provide the means to transition it to ever-changing business world.