FAPPENDL(FID, ARG1, ARG2, ...) is the same as
FPRINTF(FID, '%s\n', [ARG1, ' ', ARG2, ' ', ...]) and hence provides an
intuitive syntax for writing lines to a file. When all you need is write
a single line to a file, the original syntax provided by FPRINTF becomes
quite cumbersome. The best way is illustrate by an example.

First write a file 'fname1.tex' using FPRINTF:

pgffile = 'drawing.pgf';
fid = fopen('fname1.tex', 'w');
fprintf(fid, '%s\n', '\documentclass{article}');
fprintf(fid, '%s\n', '\usepackage{pgf}');
fprintf(fid, '%s\n', '\begin{document}');
fprintf(fid, '%s\n', ['\input{', pgffile, '}']);
fprintf(fid, '%s\n', 'Sample text');
fprintf(fid, '%s\n', 'Sample math $\langle X(t)\rangle$');
fprintf(fid, '%s\n', '\end{document}');
fclose(fid);

Then write another file 'fname2.tex' with the same content but using
FAPPENDL:

fid = fopen('fname2.tex', 'w');
fappendl fid \documentclass{article}
fappendl fid \usepackage{pgf}
fappendl fid \begin{document}
fappendl(fid, ['\input{', pgffile, '}'])
fappendl fid Sample text
fappendl fid Sample math $\langle X(t)\rangle$
fappendl fid \end{document}
fclose(fid);