Is Sicilian defense really useful
Yes, Sicilian Defense is useful, it is the 2nd best defense after 1 e4 e5.
For development 1...e5 is better: opens the diagonal of Bf8.
The Sicilian is asymmetrical and thus sharper.
After 2 Nf3 and 3 d4 black gets an extra pawn in the center, which is an advantage for the endgame, but white gets a lead in development and attacking chances.
The Sicilian isn't more complex than 1. e4 e5, that's just a bizarre myth.
After 2 Nf3 and 3 d4 black gets an extra pawn in the center, which is an advantage for the endgame, but white gets a lead in development and attacking chances.
The extra center Pawn is a middle-game advantage.
White gets a better opening, Black has better prospects in the middle-game, once he succeeds in neutralizing White's early advantage.
In the endgame, a central Pawn majority is NOT an advantage. It will LOSE to an off-side Pawn majority (usually referred-to as a "queenside majority", because K-side castling is the norm thus making the Q-side into the off-side).