The Directory Size utility is extremely useful in determining the total size of all files in any given directory or subdirectories. This function can be launched via the Tools - Directory Size menu item.
With the Standard Windows Explorer, it is impossible to determine the actual disk space used by a folder or directory unless you go into each subfolder contained in that directory and manually add up all the file sizes. This great feature of UE allows you to quickly determine the exact disk space used by any directory and/or subdirectories. It will also show you the size of the Hard Drive, the amount of space used, the amount of space free, and the amount of space the selected directory is using and the percentage of the Hard Drive that is.