Both Nikon S630 and Nikon P340 have 12.0 MP resolution sensors but Nikon S630's sensor is 1/2.3-inch (6.08 x 4.56 mm ) and Nikon P340's sensor is 1/1.7-inch (7.44 x 5.58 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 Nikon S630.
Below you can see the S630 and P340 sensor size comparison.
As seen above, Nikon P340 has a 1.5x Larger sensor area than Nikon S630. 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.