\documentclass[]{article}

\begin{document}

\newcommand\nttnob{\tt}
\newcommand{\nttb}{\tt}
\providecommand\pttnob{\tt}
\providecommand{\pttb}{\tt}

newcommand with no braces: {\nttnob text}

newcommand with braces: {\nttb text}

providecommand with no braces: {\pttnob text}

providecommand with braces: {\pttb text}

\end{document}
