Consider in the above example fremont-hypnotherapy-for-stress.com with and without the "www".   By default, www.fremont-hypnotherapy-for-stress.com will generate SEO links to "www." form of its name and the non-www fremont-hypnotherapy-for-stress.com will have SEO links to the non-www form of its name.

You might want to choose a winner among these and have, for example, the non-www form of the domain generate SEO links not to itself but to the "www" form. You can do this with a second ":" in the spec.
    fremont-hypnotherapy-for-stress.com:1_3_5,
generates SEO links to itself, but
    fremont-hypnotherapy-for-stress.com:1_3_5:www.fremont-hypnotherapy-for-stress.com
generates links to the "www." form, perhaps raising its search visibility.

You can also do this seasionally.   What if a site had the domains
   austin-pateo-supplies
   austin-christmas-store
for a business that was pateo stuff in the summer and Christmas stuff at other times.
You could have the christmas-store domain generate links to the pateo domain when it is pateo season, and vice versa in Christmas season.

You can also do this with junk domains.  If you have a domain, you might as well have it be throwing links to what you want to be visible.