A while ago we have seen that Felix has made some general decisions according to his opening repertoire:http://www.chess.com/article/view/how-to-build-up-an-opening-repertoire
Now he starts concretely with 1. b3 e5, which is presumably the most frequently played line. Ok, 2. Bb2 is clear, but now 2. ... Nc6. Black starts to build up a strong center. Are you worried? So , there is nothing wrong to give the center to your opponent. King`s Indian Players do it almost all the time. (F.e: d4 g6 2. c4 Bg7 3. Nc3 Nf6 4. e4 d6 5. Nf3) The idea is to attack the center later.
3. e3 d5 4. Bb5 Bd6 5. f4!?
Black has started to build up a strong center, but White attacks it immediately.
a) 5. ... f6
Black tries to hold the strong center!
6. Qh5+ g6 7. Qh4 exf4
So, you see that the Bb2-diagonal has gone open. Not too bad, or?
I recommend this pawn sacrifice for quick development. There is one game in database and Black refused (!)to take the pawn. Otherwise the dangerous f-file would have been opened and Rf1 in indirect contact with Kf7
So, you see that white has an interesting plan in this line. When Felix showed this line to his friend Amando, a much higher rated player, he got the answer: "Well, it looks OK. But may be the pawn sacrifice can be played in combination with long castling!" Felix looked puzzled:"How do you mean?" "Well", said Amando, "may be 9. Nc3 instead of 9. 0-0. Then you can play 10. 0-0-0 and your king side attack will be much stronger, because your king is out of the way."
Felix smiled:"That`s a fantastic idea! You are genius!" Amando shook his head: "No, no, this is only an idea. You have to check it with your engine!" "OK. I will do!", Felix answered. "Let´s start a game with this line. You take the Black ones!"