Both Nikon P340 and Olympus XZ-10 have 12.0 MP resolution sensors but Nikon P340's sensor is 1/1.7-inch (7.44 x 5.58 mm ) and Olympus XZ-10's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Nikon P340's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Olympus XZ-10.
Below you can see the P340 and XZ-10 sensor size comparison.
As seen above, Nikon P340 has a 1.5x Larger sensor area than Olympus XZ-10. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.