The current date, local time zone. Subject to the timefmt parameter to the config command. The last modification date of the current document. Subject to timefmt like the others. Frequently-used applications of SSIs.
Some people like to have the current URL for any page be on the document.
Say you wanted to have a standard footer on every page, much like you can do with a word processing package. You'd have to edit ALL of your HTML files. That is, unless your footer text was located in another file. For more infomration on SSIs, go to NCSA's tutorial .