From the answer to my other question " How can I define a math operator behaving like \lim or \sum with limits?", I tried:
In " What is the difference between \def and \newcommand?", it is said that they are basically the same and
\newcommand is a bit more clever and does some extra checks. But it suggests that they should behave in just the same way.
But actually they do not. For the
\def case, it seems to add extra spacing around
\ext when I use it (just like
\lim would). And
\newcommand does not.
Why? What exactly is the different behavior for those more generally?