You set the paragraph indentation to be 0em. Hence, using \indent
would leave a horizontal space (or indent) before a paragraph of
exactly 0em, or nothing. Remove \parindent0em and you'll notice the
difference when using
\indent INDENT & & \\
instead of
\mbox{ INDENT} & & \\
Other alternatives also exist. For example, using
\hspace{2cm}INDENT & & \\
\hskip 2cm INDENT & & \\
or you could even set a column with a specific width (like p{2cm}) to
obtain a certain, fixed indentation per line.
Werner