Both uses are sufficient in the context you show, since they produce the same result:

However, in a slightly different context - removing the punctuation !
immediately following the macro use, the results are noticeably different:

\documentclass{article}
\newcommand{\Variable}{World}
\begin{document}
Hello \Variable{} Welcome!!
Hello \Variable Welcome!!
\end{document}
With {}
the inter-word space is preserved, while it is gobbled when using \Variable
without {}
. This is due to the way TeX reads the input stream to identify where a macro ends.
Which is "more correct"? It depends on the context as you can use it - the ending braces {}
- in some places, but it's not always necessary.
Relevant contents to read:
Technically you can place your \newcommand
wherever you want. It is better practice to separate document structure from content. Therefore, it is customary to include all command definitions and document formatting content as part of the preamble - between \documentclass
and \begin{document}
.
This remains, however, purely a suggestion and depends on the end user. Some people may feel more inclined to keep definitions together with their usage (if the document provides that "flow"), others roll the more conventional way.