In my area (computer science) it is standard to publish several papers during the course of your PhD and then only "write" your thesis in the last few months of graduate school --- often you only start compiling the thesis once you have secured a job for after graduation.
I realize that in other areas this is different --- your thesis is the primary output of your time in graduate school. However, in my area the primary output is the papers you have published and the thesis seems redundant.
Given that all the content of my PhD thesis already exists in published papers, what is the point of writing the thesis (other than to fulfill the university's requirements)? Why would someone (other than my committee) read my thesis?
I want to know what it is that I am trying to achieve when writing my thesis (as I am currently starting this process). Thus, an alternative question would be: How do I write a good/useful thesis, given that I have published all the results it will contain?
All of my papers have full versions on arxiv, which contain discussion of motivation, background, and related work, as well as all the details and some side results. (Unlike, say, mathematics papers, which tend to be very terse.) So in terms of exposition, I am not sure what would be added in my thesis.