Some versions of TeX, namely pdfTeX and LuaTeX, have microtypography features. These involve stretching font glyphs slightly, and allowing text to produce very slightly into the margins. Use of these gives TeX more flexibility in breaking a paragraph into lines, and can improve paragraph appearance by reducing hyphenation and producing a more consistent typographic color.
texinfo.tex uses these features (‘microtype’ for short) when available. You can turn microtype off by specifying ‘@microtype off’ in your input file; likewise, ‘@microtype on’ turns microtype back on.
The fonts used in LaTeX output may not be scalable. If fonts are not scalable, using microtypography could trigger an error when converting the LaTeX output. Therefore microtypography is not turned on in the default case in LaTeX output. It is possible to turn it on with ‘@microtype on’. A way to get scalable fonts for the font used in the default LaTeX output is to install the CM-Super font package (http://ctan.org/pkg/cm-super).
The @microtype command does nothing for other output formats.