The e5 move opens diagonals for both the Black queen and the kingside bishop and important stakes a claim to d4. Now White has to worry about Qh4 later on. White already has the worse position, with trouble developing and putting pressure on the center, especially d4, and with many kingside weaknesses. This is not a desirable position for white, which is why 1.f3 never occurs among serious chess players.

Of note here is the blunderous move 2. g4??, which allows 2...Qh4#, the fastest possible checkmate.

Wikipedia has related information at Barnes Opening.

• Nunn's Chess Openings. 1999. John Nunn (Editor), Graham Burgess, John Emms, Joe Gallagher. ISBN 1-8574-4221-0.
• Modern Chess Openings: MCO-14. 1999. Nick de Firmian, Walter Korn. ISBN 0-8129-3084-3.