I apparently can't see the difference in a compilation (pdflatex) between
\operatorname. So, as in the title the question is: is there a difference? Which one is preferable in what occasions?
There are many differences. The main one is in the fact that
where it's clear that the second line is wrongly typeset. Even if your "operator" requires parentheses after it, it should be
Another subtle difference is in how some characters are interpreted in
and now it's clear what is to be used. Indeed
It is like math mode (no spaces), but in upright mode. The font size isn't changed.
The argument is written in upright mode but with some additional space before and behind.
The following example shows the differences:
gave the equivalent output as