There are times when an author needs to insert text into math. The
\rm command only switches to the Roman font for math letters. It
does not, for example, let you print a normal text hyphen: ${\rm e-p}$ gives ``e - p''. Using an \mbox{#1} will give you normal
text, including a hyphen, but will not scale correctly in superscripts:
$x_{\mbox{e-p}}$ gives ``
xe-p''. The \text{#1}
command will solve both problems. It gives you regular text and
scales correctly in superscripts: $y=x \text{ for } x_{\text{e-p}}$
gives ``
y = x forxe-p''.