savebox for more complicated examples

\sbox accepts paragraphs in its argument but it is a horizontal box like \mbox so you need a nested \parbox.

\documentclass[12pt,oneside]{article}
\begin{document}

{This is a paragraph.}

{This is another paragraph.}

\newsavebox{\temp}
\sbox{\temp}{%
\parbox{\textwidth}{%
This is a paragraph.

This is another paragraph.
}}

\noindent\usebox{\temp}

\end{document}