The {memoir} document class allows for text smaller than \tiny, with the \miniscule command, which can be useful, but I never find myself needing to write an actual memoir. I tend to use either {article} or {\standalone}, or a combination of the two. For instance I might start an article and as the main file, draw standalone diagrams in separate files, and insert the graphics with something like:
\noindent\makebox[\textwidth]
{\includegraphics[scale=0.8]{illustration.pdf}}
After all, the best thing about vectors is they're scalable.
Here's a quick demo of a situation where \miniscule text might be useful:
It looks okay, but I want to make the [32-bit] text smaller:
(\textcolor{red!50!black!50}{\tiny{[32-bit]}})
%%% Document Preamble %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\documentclass[varwidth]{standalone}
\usepackage{tikz, xcolor}
\usetikzlibrary{arrows, arrows.meta}
\begin{document}
%%% Tikz Preamble %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Set Default Arrowheads, Node Distance, etc.
\begin{tikzpicture}
[-{>[scale=3,length=width=2]}, >=Stealth,
node distance=15mm, auto]
%%% Define Object Types %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\tikzstyle{red_ball} = [draw, circle, fill=red!20,
text width=1.5em, minimum height=2.5em, text centered]
\tikzstyle{blue_ball} = [draw, circle, fill=blue!20,
text width=1.5em, minimum height=2.5em, text centered]
%%% Place Nodes %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Associate Objects with Text
\node[red_ball](Pbi) {$P_{\beta_{i}}$};
\node[blue_ball, below of=Pbi](XOR) {$\oplus$};
% Additional Annotations
\node[yshift=12mm, below of=Pbi](PbiBits)
{\textcolor{red!50!black!50}{\tiny{[32-bit]}}};
%%% Draw Lines, Arrows, etc. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\draw[->](Pbi)--(XOR);
%%% Close Tikz Environment %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\end{tikzpicture}
%%% Close Main Environment %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\end{document}


\tiny{[32-bit]}should be\tiny [32-bit]font sizes do not take an argument you could use\fontsize{3pt}{4pt}\selectfontwithfix-cmpackage if you use the standard cm fonts – David Carlisle Jul 10 '19 at 16:44fix-cmpackage but it seemed to go ignored. I think Computer Modern fonts are the default; I haven't changed them. I'll try again, thanks. – voices Jul 10 '19 at 16:51\tiny{one} two threeto just makeonetiny but it applies to two and three as well. without fix-cm your will get font substitutions to a fixed set of sizes for cm, and will not be able to go below 5pt – David Carlisle Jul 10 '19 at 17:30