Sankaku Channel/

I've just noticed this, but why do seiyuu have character tags and why are they used to tag characters they voice?

Example: fukuen_misato

Yes, I know she voices Golden Darkness and Yoshika, but she is not physically present in images so I see no purpose to put her tag in there, unless it's for seiyuu_connection.. but then again, I think that seiyuu should get their own tag color.