The extract action is provided to help people who want to apply the changes on the resource to some location.
The changes are applied with respect to the hierarchical structure of the selection.
If the change is the deletion, than the existing resource in the location with the same path will be deleted.
Otherwise the existing resources will be replaced and the others will be created.
The usage area of this action is quite wide. For example the team is developing a web site. When all the proper changes are made the web master can apply them to the whole site by just one click. The only thing to do is to select in the history of the site the current state and the newer one. After that by clicking on 'Extract...' in drop-down menu and selecting the site root directory as a location the site becomes up to date.
In Synchronize View you have a probability to extract local changes, remote changes or both.
Using local extracting will apply your local changes comparatively to the base revision to the specified location. Using the remote one will apply the incoming changes to the specified location. 'Extract All' action provides a probability to apply both local and incoming changes, but it is disabled if the selection contains conflicting changes. To enable it you should merge the conflicts before extracting.
In History View extracting is possible both when two remote revisions are selected or when one. The changes are gathered between the selected revisions or between the single selected revision and the previous one and then applied to the specified location. Pay special attention to the fact, that while viewing history of the remote resource the remote container name is used for extract, but not local one.