Activating the "Allow per-URL settings" button allows you to save KDE settings (e.g., whether menubar, toolbar, statusbar, and URL are shown or hidden, the window size, all the options from the 'View' menu, ...) as settings for a given URL. This can be, for example, any directory on your disk where you have write access, or any URL (directory or even Web URL) which has a shortcut on your desktop or which you have bookmarked.
One of the KFM File Manager features is to display a view of the directory tree in the left part of its window if "Show Tree" in its "View" menu is enabled. If the "Tree view follows navigation" option is selected here, the tree view of directories you enter by clicking on their icons in the right part of the File Manger window will appear, and will continue to be displayed after you leave the directory. You can then return to a previously-entered directory easily, by clicking on its entry in in the tree.
You may also specify the terminal and editor applications that may be invoked by the File Manager:
In the "Terminal" box, you can enter the command that will be executed to provide a terminal whenever you select "Open Terminal" in the File Manager "File" menu, or when an application is about to be run in a terminal by the file manager. The default terminal application is konsole.
In the ``Editor'' box, you can enter the command that will be used to start an editor to view html source when the File Manager's View Frame Source or View Document Source ``View'' menu items are invoked. The default editor is kedit.