Yes, it does. The difference between \small and \normalfont is just not very large, so you maybe just didn't notice it.
There are in general two ways to go (and your example contains both):
- set a fontsize (
\small, \tiny, etc.) before the \begin{tabular}, then all cells will have this fontsize
- use the fontsize only within a cell, then only this cell will have this fontsize
Note also: If you apply \small for the whole tabular, and you want a specific cell to be even smaller, then you need to use an even smaller fontsize in a specific cell (like \footnotesize).
See here an example of how the different fontsizes look like in a table:
\documentclass{article}
\begin{document}
\normalsize
\begin{tabular}{|p{2cm}|p{6cm}|}
\hline
\textbf{Symbol} & \textbf{Description} \\
\hline
$E_{c , TL}$& Total energy consumption in a day \\
\hline
\end{tabular}
\small
\begin{tabular}{|p{2cm}|p{6cm}|}
\hline
\textbf{Symbol} & \textbf{Description} \\
\hline
$E_{c , TL}$& Total energy consumption in a day \\
\hline
\end{tabular}
\footnotesize
\begin{tabular}{|p{2cm}|p{6cm}|}
\hline
\textbf{Symbol} & \textbf{Description} \\
\hline
$E_{c , TL}$& Total energy consumption in a day \\
\hline
\end{tabular}
\scriptsize
\begin{tabular}{|p{2cm}|p{6cm}|}
\hline
\textbf{Symbol} & \textbf{Description} \\
\hline
$E_{c , TL}$& Total energy consumption in a day \\
\hline
\end{tabular}
\tiny
\begin{tabular}{|p{2cm}|p{6cm}|}
\hline
\textbf{Symbol} & \textbf{Description} \\
\hline
$E_{c , TL}$& Total energy consumption in a day \\
\hline
\end{tabular}
\end{document}

\documentclassand ending with\end{document}. – Bobyandbob Jun 13 '17 at 13:18