To achieve a very similar goal I generally use the following:
\begin{frame}
\frametitle{Size changed}
\scalebox{0.8}{\begin{minipage}{1.20\textwidth}
... your content here ...
\end{minipage}}
\end{frame}
I do not know how to compute the combined values of the scale factor and of the minipage width, I generally try several values until it satisfies me.
For example, the following content:
\begin{itemize}
\item First item.
\begin{itemize}
\item First subitem.
\begin{itemize}
\item \lipsum[75]
\item \lipsum[66]
\item \lipsum[75]
\end{itemize}
\item Second subitem.
\end{itemize}
\item Second item.
\item Third item.
\end{itemize}
gives:

and if you change the scale/minipage values to 0.6/1.6 you obtain:

For a centered table I use:
\begin{frame} {Scale Items}
\makebox[1.1\linewidth][c]{\scalebox{0.8}{\begin{minipage}{0.8\linewidth}
\begin{tabular}{l | c | c | c | c }
& Column1 & Column2 & Column3 & Column4 \\
\hline \hline
Line1 & Value11 & Value12 & Value13 & Value14\\
Line2 & Value21 & Value22 & Value23 & Value24\\
Line3 & Value31 & Value32 & Value33 & Value34\\
Line4 & Value41 & Value42 & Value34 & Value44
\end{tabular}
\end{minipage}}}
\end{frame}
which leads to:

and if you change \scalebox{0.8} to \scalebox{1.2} then you will have the following result:

shrinkandsqueezeoptions suffice? They are in beamer manual, page 61, section 8.1. – Rmano Jun 08 '16 at 15:48\resizeboxfor tables as suggested here: http://tex.stackexchange.com/questions/5067/shrinking-tables-for-presentations – m13r Jan 20 '17 at 07:32