What are the implications of changing "Primary Mapped Domain?"

Hello,

It would be nice if we could upload screenshots when 1st creating an issue. (hint, hint)

In the domain mapping list of mapped domains there is a star icon and hovering over it indicates that clicking it will change your primary domain.

What exactly does that mean and what are the implications of clicking the star?

I could not find any reference to this in the usage documentation unless I overlooked it.

Please advise.

Thanks,
Phil D