To be able to configure in one place settings that applies to different siteaccesses which can't be set in override settings because it doesn't apply to all of them (ex: admin).

One solution would be to think about the inheritance concept:

/settings/siteaccess/website/
/settings/siteaccess/admin/
/settings/siteaccess/plain/
/settings/siteaccess/eng/
/settings/siteaccess/fre/
/settings/siteaccess/ita/

Siteaccesses "eng", "fre" and "ita" could inherits from "plain".
Siteaccesses "plain" and "admin" could inherits from "website".

Those "virtual" siteaccesses may be located elsewhere for clarity, ex:
/settings/virtual/website/
/settings/virtual/plain/