Purpose of foreign link?

[vishes-shell]

I am paying my respect to the creators and contributors of that extension, but i am not quite getting what foreign_link for? Because if there is foreign link, the link that should lead to specific static content would lead to that foreign link. I am sure that there is some purpose of it. but i am little confused, should i have that field or not. To be clear, that is absolutely not an issue, just a question.