In relation to the size of fonts I used to regard something like \Huge as a switch, \Huge{<some text>} as restricted to <some text>. Apparently not so. It turns out that proper grouping requires {\Huge ...}. I just wondered what the distinction there then is between switches \Huge <some text> and \Huge {<some text>}, if any.
\documentclass{article}
% RN. 03 Dec 2018
\begin{document}
\Huge{Huge}
Huge persists
\tiny{tiny}
tiny persists
\normalsize
normalsize
{\Huge{Huge}}
Huge properly grouped
{\Huge Huge}
Huge properly grouped, again
\end{document}

\Huge ...is equivalent to\Huge {...}(except in some corner cases, but these are not related to the presence of\Huge). – Henri Menke Dec 03 '18 at 03:44\Hugeis one) persist until the local group they appear in is closed. This is the reason why your{\Huge ...}example works as expected, the\Huge{...}example, on the other hand, doesn't. In the latter case, the effect persists until the\endgroupused internally by\end{document}occurs. – siracusa Dec 03 '18 at 03:56