This unified navigational scheme allows readers to wander through Webspace using the navigational skills they've already learned at other Websites. Essentially, frames require readers to alter their navigational strategies and behaviors, to varying degrees, at each new site they visit. It's hard to imagine a more genuinely calamitous prospect for the Web and its users. URLs allow a given document to be associated with a uniquely identifiable name. Thus, breaking URLs on the Web is roughly equivalent to removing the titles from all the books in a library.
Search engines can also break, for much the same reason.
It's possible , for example, to repair URLs, but the mechanics of URL repair are cumbersome and awkward. Thus frames complicate not only the use of a site, but also its design. After all, they forcibly resist all attempts to connect their contents to the larger WWW, and they require users to navigate via their elaborate, idiosyncratic menu system. Ironically, frames are most commonly used to create a separate pane containing various navigational links. But these separate links cannot substitute for navigational links embedded on the constituent pages themselves.