Black has placed a pawn in the centre of the board, gaining space and taking over the d4- and f4-squares. Black also discourages the natural 2. Nf3, as Black will simply kick the knight with a further pawn advance. 1. g3 e5 2. Nf3 is still sometimes seen anyway, and is known as the Reversed Alekhine, as the strategy from this opening is similar to Alekhine’s Defense but with the colours reversed. More commonly, White will either continue developing with Bg2, Nf3, O-O, etc. and adopt a King’s Indian Attack setup, or will strike back in the centre immediately.

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1.g3 e5

Wikipedia has related information at Benko Opening.

• Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.