If I think there's too much space between the $V$ and the , in $V$,, what's the best way to reduce it? It seems safe to use \kern and not safe to use \hspace, since if you use \hspace the line might break between the $V$ and the ,:
\documentclass{article}
\begin{document}
%line broken between $V$ and ,
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~%
For all $V$\hspace{-1pt}, the theorem holds.
%line broken between "all" and "$V$\kern-1pt,"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~%
For all $V$\kern-1pt, the theorem holds.
\end{document}
But is there a better way?

\kernis the proper way to do it (not\hspace) and for the reason you cite. Whether there is way to automate, short of rekerning the font, I do not know of any. – Steven B. Segletes Feb 26 '14 at 18:53$y=x\,$,) so that the comma doesn't intrude on the math code. For$V$,it is fortunate I wouldn't have to do that. – Dan Feb 26 '14 at 19:50\mathsurroundprimitive. I find that\mathsurroundis far too indiscriminant and manually insert a little space when I think it is useful to improve readability. Despite your eight exclamation points (clearly added only to meet the minimum character requirement), I don't find$V$,has too much space (maybe a little more than is optimal, but not that bad). – Dan Feb 27 '14 at 23:10