SHTML files are HTML files with SSI (Server Side Includes). SSI allows to include a common fragment into several HTML files, etc. Using Client Side SSI, you can convert SHTML files to plain HTML files. This can be used both for testing SHTML files (before placing them to a web-server) and for developing plain HTML files (avoiding duplicate HTML fragments, etc.). Also it can be used for converting an SSI-web-site to non-SSI-web-site.