The variation goes(I will do it through the scotch gambit)
[fen "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR b KQkq - 0 1"]
1.e4 e5 2.Nf3 Nc6 3.d4 exd4 4.Bc4 Bc5 5.c3 Nf6 6.cxd4 Bb4+ 7.Kf1 (7.Bd2)(7.Nc3)
I suppose the alternative is to play Bd2, but I believe that black manages to often hold a draw here because of theoretical repetition lines. White could of also played Nc3, though tricky, Black seems to be doing fine if they know the theory. Thus, it seems like Kf1 is played to avoid a draw. However, if avoiding a draw is desired, why not simply play e5 instead of cxd4? Is there really anything in this Kf1 variation or is it harmless?