What this does is replaces the \tableofcontents command with a definition that selects the font size for nothing, and does not produce any table of contents at all.
The real \tableofcontents command reads the \jobname.toc file and processes all the commands in it. If Beamer is working like normal LaTeX,each of them probably sets its own font size, so if you wanted to reduce the size of them all you would need to redefine all of them individually.
You have several choices:
- Reduce the number of sections and subsections in your presentation.
- Set the tocdepth counter to a smaller value so that it only produces entries for sections, not for subsections as well.
- Redefine the \beamer@sectionintoc and \beamer@subsectionintoc commands to use a smaller font and smaller inter-line spacing
- Try enclosing the \tableofcontents command in a \vbox and applying the \scalebox command from the graphicx package (I have no idea if this will work), eg \scalebox{0.8}{\vbox{\tableofcontents}}
- Try enclosing the \tableofcontents command in a font-sizing group, eg {\tiny\tableofcontents}
- If the ToC has short entries, maybe try putting it into columns, eg \begin{multicols}{2}\tableofcontents\end{multicols}
///Peter