Why the * in \newcommand*?

Question

I saw several examples of user defined macros using \newcommand (without the *), and examples with \newcommand*. Trying both in my test documents doesn't show any difference. So why the asterisk? What are its functions? Should I care about it or not?

Here's a simple MWE to play with, in case it is usefeull here:

\documentclass[11pt,letterpaper,twoside]{book}
\usepackage{lmodern}
\usepackage{amsmath}
\usepackage{mathtools}

\newcommand*{\bigs}[1]{\vcenter{\hbox{\scalebox{1.25}{#1}}}} % Why the *?

\begin{document}

Blabla bla bla blabla :
    \begin{equation}
        c \, \bigs( 1 + (x - y^2)(a + b) \bigs) = \tfrac{3}{4}.
    \end{equation}

\end{document}