In e4 e5 lines I've started my opponents are often careless with their e5 pawn.
1. e4 e5
2. Nf3 Nc6
3. Bb5 d6
4. d4 a6? (exd4 or Bb7)
5. Bxc6 bxc6
6. dxe5
Black to move.
6...dxe5
7. Qxd8+ Kxd8
8. Nxe5
Is clearly terrible.
6... Bg4
7. exd6 cxd6
Black is just down a pawn.