This feature is very useful when developing pages. After you make a change on a site/page, you often want to reload the page to see/test your changes. But, depending on the cache directives your site sends (or how your browser caches local pages), when you reload the page, you might get and old, cached version instead. And, in Firefox for example, filled-in forms won't be cleared.
This is where Ctrl + F5 comes in. It totally reloads the page (clears forms and all) and gets a fresh version of the page from the server/file (by sending the proper cache directives int he request headers or overriding the cache. See the stackoverflow link above).
Unfortunately, Opera doesn't support this at all (it's bug CORE-32618) and often, Opera makes it a pain to get the updated version of the page. Every time you make a change to a page on a site, you have to delete the cache first before you reload or you'll get a cached version.
Other browsers have supported this for a long time.