Another example is a recent game I played using the anti-Sicilian Morra gambit:
Basically, the gambit is 1.e4..c5 2.d4...cxd4 3.c3...dxc3 4.Nxc3
So, white has stopped his opponent playing his cherished Sicilian & developed his queenside knight to it's best square & has a foot-hold in the centre with the e4 pawn.
I had gained a tempo & development for the cost of a pawn.
Being 2 moves ahead so early in the game is a big advantage, especially if you are playing a Sicilian player who is unfamiliar with the Morra gambit - they are in your domain now!
I then brought my bishop out to c4, preventing black playing d5, developed my g1 knight to f3, castled etc.
The idea is to control the 1/2 open c & d files with the rooks & attack blacks kingside (where he will normally castle) with my other pieces using the developmental advantage.
If you look at the example game Game 2717523
you can see by my (white's) 9th move I have far more active pieces, I also have his d5 pawn pinned against his queen.
By contrast, his bishop on c8 has nowhere to go, his queen has few good squares & I'm about to try to blow-open the centre with my rook & queen bearing down on the d & e files which could result in a very early, bloody win.
He struggled on a while after I had promoted my a-pawn on move 37, resigning soon after.