\input and \include are different in Latex

http://www.ics.mq.edu.au/~rdale/resources/writingnotes/latexstruct.html

\documentstyle{...}
...
\includeonly{secondfile}
...
\begin{document}
\include{firstfile}
\include{secondfile}
...
\include{lastfile}
\end{document}
This tells LaTeX to consult the aux files corresponding to each included file, but only to actually include the text of the files listed in the \includeonly line. Because LaTeX looks at the other aux files, it knows about section and page numbers, cross-references, and so on. This means that the output will start at the appropriate page for the text in secondfile.tex, with appropriate section numbers and so on. Simply by changing the \includeonly line and reformatting, you can get different parts of the entire document printed, with all the numbering being that which you would get had you printed the entire document.
One potential disadvantage of this method is that, unlike \input, each included file will automatically begin on a new page