If you compare resampled and 1:1 sections, you'll see that on resampled image the noise level is lower.

By today's consumer digital cameras different ISO settings are available but this still hasn't a lot advantages comparing to classic film photography. Really, at higher ISO level, more closed aperture or shorter shutter time could be used for night or lowlight exposures but the noise of the picture increases a lot. When images are resampled to smaller dimension, the noise is less visible.

Sensitivity (ISO)

This clipping shows how the noise becomes visible when the sensitivity is set to ISO 800.  Section data:

Resampled to

not reduced (screen size 1:1)

Resample process

not resampled

Compression

30 steps

Original image data:

Type

fine JPEG

Resolution

2560*1800

File size

2904 KB

Image size/72dpi

903x677mm

Focus

200

Aperture

9,5

Shutter time

1/250 sec

ISO

800

White balance

Daylight

Color

0

Intensity

0

Contrast

0

Sharpness

Normal

 

Default settings