This option configures the crawler to follow links a specific "distance" from the start URL(s).
If this option is set, then the crawler will run in single-threaded mode (i.e. only one web connection will be made at a time) to control which URLs are processed. This will have an impact on performance i.e. slower crawl.
Limit the crawler to the URLs linked to from all URLs listed in the
Limit to all pages linked to from set 1: