They are used as part of the FrontPage server side extensions which do
- change tracking (mostly the
_vti_cnf) - code/script used by FrontPage specific controls (mostly the
_vti_script) - general settings
The old FrontPage program and Dreamweaver both used it.
The VTI part is actually because FrontPage was originally created by Vermeer Technologies Incorporated (note the acronym) and then bought by Microsoft and it just stuck.