I know the general purpose of relative clauses and how to construct them, but lately I've seen them being used in this way,
Der Mann da, der guckt dich immer an
to mean "That man over there is always looking at you".
To me this German sentence translates to "That man there, who is always looking at you" which I understand doesn't make sense on its own, but I'm confused as to why someone would choose to use a relative clause this way as opposed to "Der Mann da guckt dich immer an". Is this a usual way to construct sentences? What is the difference between this relative clause construction and "Der Mann da guckt dich immer an"?
EDIT: As a poster below pointed out, I realize now this was a poor example because this was not a relative clause. There are other examples though, where I have heard actual relative clauses used this way. The main example is the Fettes Brot song "An Tagen Wie Diesen"
Niemand, der mir sagt, wieso Beim Frühstück oder Abendbrot Die Fragen bohren so gnadenlos
which is supposed to mean "No one tells me why these questions persist at breakfast and dinner"