Use "parts" in a master thesis report I am writing a master thesis of about 80-100 pages and want to know a good way of structuring my document either using only chapters or chapters and "parts". f first wanted to post this question to the TeX Stack Exchange but realized that it was too philosophical. 

As most thesis writers I use LaTeX and I have seen thesis templates that use \part (classicthesis) and ones that do not (master thesis template from a university). I think that classicthesis is mostly aimed at PhD thesis documents that are longer and will become a "book".

So when is it appropriate to use \part? Any specific document length in pages or number of chapters? 

When you use \part then a page is cleared after the text. Is this a style that is used in American PhD thesis documents? Why is this done?

I have also looked at some textbooks and they often do not have something similar to part. Instead these books only use chapters. One of my favorite textbooks (Artificial Intelligence: A modern approach by Russel) uses parts but no actual pages that show the parts name. Instead they are only visible in the table of contents.

My two competing ideas are with and without parts:

   \chapter{Introduction}
\part{Concepts}
   \chapter{Background}
   \chapter{Related work}
\part{Methods and systems}
   \chapter{Proposed method}
   \chapter{Implementation}
\part{Evaluation}
   \chapter{Experiments}
   \chapter{Analysis}
\part{Conclusions}
   \chapter{Conclusions}
   \chapter{Future work}
So when is it appropriate to use \part? Any specific document length in pages or number of chapters?


It is appropriate when you feel it appropriate! Seriously though, assuming that there isn't any guideline from your university (otherwise, you probably wouldn't be asking the question), it's really a personal choice, the same than about the splitting chapter/section/subsection/subsubsection/paragraph. The structure of a document is there to help the reader, in particular for long documents. A part could be something that can be read separately (i.e., with no references to the other parts), or could be something containing some huge chapters; tt could reflect a chronological order (before, during, after), or a conceptual separation (theoretical, applied), etc. 

In case of doubt, talk with your advisor!


  When you use \part then a page is cleared after the text. Is this a style that is used in American PhD thesis documents? Why is this done?


As @Daniel pointed out, this is a rather technical question, that is more likely to be answered on tex.SE.