[texhax] Roman subscripts

[Paul Wagner]

Hi TeXnicians,

I often need to type subscripts in math mode that are roman instead of
italic. To avoid having to do a \mathrm every time, I defined

\catcode`\_=\active
\def_{\sb\mathrm}

so I can have roman subscripts with $X_{ff}$ and italic subscripts with
$X\sb{ff}$.

My question is: Since I have some experience in using TeX, but very little
experience in programming TeX, are there any disadvantages to this method?

Thanks,

Paul