When should we use \begin{center} instead of \centering?

Question

After reading this question Should I use center or centering for figures?, I want to know the answer of the following.

When should we use \begin{center} instead of \centering?

For example, should we use this one?

{%
\centering
<other contents>
}

or this one?

\begin{center}
<other contents>
\end{center}

Answer 1

First of all, \centering needs a \par (or an empty line) before the closing brace

{\centering
  contents\par
}

Usually it's used inside some environment that provides the necessary \par, such as minipage or figure. Try

abc{\centering def}ghi

to see the effect.

The main difference with center is that \centering doesn't leave vertical space before and after it: \begin{center} is defined in terms of trivlist.

\def\center{\trivlist \centering\item\relax}
\def\endcenter{\endtrivlist}
\def\centering{%
  \let\\\@centercr
  \rightskip\@flushglue\leftskip\@flushglue
  \parindent\z@\parfillskip\z@skip}