The 6 Bc4 variation offers a variety of themes and ideas after 6...e6 7 Bb3 b5. White eyes the sensitive e6 square for possible sacrifices with either Be6 or Ne6 once Black has removed one of its protectors (either by ...Bb7 or by blocking its protection with ...Nbd7 or, in some cases, ...Nfd7).
One of White's most popular plans is to effect an immediate Kingside castle, advance the f-pawn to f4, and then, depending upon Black's responses, to advance either the e-pawn dislodging the Black King Knight or to advance the f-pawn provoking e6-e5 thereby weakening Black's control of the critical d5 square.
Black is not without his resources though. He may wish to eliminate the troublesome Bishop immediately by simply playing ...Nbd7, ...NcS and ...Nb3, though this does prove rather time-consuming. At every juncture, Black must check the validity of the b5-b4 advance diminishing White's grip on the central e4 and d5 squares after he relocates his Queen Knight. Still another Black motif is the speculative maneuver ...Bb7, ...Rc8 and ...Rc3!? followed by ...Ne4 or ...Be4. In compensation for the exchange sacrifice, Black has an extra central pawn, White is saddled with double isolated c-pawns and Black's minor pieces are more actively posted.