This option rebuilds the LaunchServices allowing to remove the links between documents and applications.
When you launch a new type of document for the first time, you are presented with an alert message. You then have several options: allow your document to be opened by the application to which the System defaulted, let the Finder display this application in its surrounding sub/folder, or cancel opening the document. Once opened a first time, the link between this type of document and the application which executed it is stored. Also stored are all installed applications, your choices of specific applications to open specific types of documents as well as your choice of a default web-browser.
After rebuilding, double-clicking documents or web-links may call unexpected applications. To change that back to your preferred settings, select a file of the desired type in the Finder, choose "File/Get Info" (Apple-I), select the application you prefer from the list of available choices in the "Open With..." menu, then click "Change All" to tell the Finder that all similar files shall call that same application. The default web-browser can be redefined in any browser's Preferences pane. It allows you to correct also misc problems: Display of double applications or deleted in the contextual menu's "Open With", Icons not in conformity of certain files and folders, launching of wrong application double-clicking on a document.
LaunchServices can be rebuiltfrom the Maintenance panel > Rebuild or from the Automation panel.
aus der hilfe von onyx...
was es im prinzip macht ist evtl. komisch gesetzte file associations wiederherzustellen.