One sentence of dummy text

With some help from xparse we can extract a rich supply of sentences from lipsum; precisely 1498, I guess they're sufficient.

\documentclass{article}
\usepackage{lipsum}
\usepackage{xparse}

% store a big set of sentences
\unpacklipsum[1-100] % it was \UnpackLipsum before version 2.0

\ExplSyntaxOn
% unpack \lipsumexp
\seq_new:N \g_lipsum_sentences_seq
\cs_generate_variant:Nn \seq_set_split:Nnn { NnV }
\seq_gset_split:NnV \g_lipsum_sentences_seq {.~} \lipsumexp

\NewDocumentCommand{\lipsumsentence}{>{\SplitArgument{1}{-}}O{1-7}}
 {
  \lipsumsentenceaux #1
 }
\NewDocumentCommand{\lipsumsentenceaux}{mm}
 {
  \IfNoValueTF { #2 }
   {
    \seq_item:Nn \g_lipsum_sentences_seq { #1 }.~
   }
   {
    \int_step_inline:nnnn { #1 } { 1 } { #2 }
     {
      \seq_item:Nn \g_lipsum_sentences_seq { ##1 }.~
     }
   }
 }
\ExplSyntaxOff

\begin{document}

\section{Seven sentences}

\lipsumsentence

\section{Three sentences}

\lipsumsentence[2-4]

\section{Some single sentences}

\lipsumsentence[1]

\lipsumsentence[2]

\lipsumsentence[3]

\lipsumsentence[4]

\lipsumsentence[5]

\end{document}

\newcount\zz
\loop
Hello world.
\advance\zz1
\ifnum\zz<10
\repeat

writes Hello world 10 times.

You can use a macro for the dummy text and a loop to repeat it, taking as an argument the number of repetitions. These commands work in any variety of TeX, but I illustrate their use in a LaTeX document.

\documentclass{article} 

% Define the dummy sentence, an ancient palindrome.
\def\sator{Sator Arepo tenet opera rotas.}

% Create a command to print the sentence repeatedly.
% Argument #1 is the number of times to repeat it.
\newcount\loopcounter
\def\dummysentences#1{%
    \loopcounter = #1
    \loop
        \sator\ %
        \advance\loopcounter by -1
        \ifnum\loopcounter > 0
    \repeat%
}

\begin{document}

\sator

\dummysentences{5}

\begin{itemize}
\item \sator
\item \dummysentences{3}
\item \dummysentences{2}
\end{itemize}

\end{document}

See also my answer here: Is there a dummy package like Lipsum or Blindtext for Tables and Figures?