When using an FTP IFS, uncached drive scanning may be extremely slow, especially when using a dialup connection. Checking this option will speed up the process of building the directory tree by eliminating the scan for subdirectories of the first level of directories. Such moding is more like that of other FTP applications. When used in this manner, the directory tree will not show expandable directories with the expand control until that directory is read.
See FTP Use and Support for additional information.