As default a WordPress installation use a wp-content directory which store themes, plugins, media files, cache data etc. This option allow a way to change this slug to something else on front side html.
New Content Path
A theme file loaded from default wp-content folder appear like this:
After filling in this option e.g. general-data the links will change to this:
If a theme slug was also specified for the theme (see Rewrite – Theme) the urls will use just the new slug.
Block wp-content URL
After changing the default wp-content to something else, the old urls are still accessible. This provide a way to deny all old urls by returning default theme 404 error page.