A slightly soft image can look crisper when neighbouring pixel differences are emphasised. Sharpening changes that edge contrast. It does not turn a low resolution source into a genuinely more detailed photograph.
Image Sharpening applies a fixed sharpening convolution. There is no strength slider in this tool, so each run performs the same defined filter operation.
Examine a high contrast edge
An edge between a dark label and a light background is a useful place to inspect the change. Look for improved definition, then check whether a bright or dark halo has appeared around it.
The image retains its original width and height. A 400 by 300 source stays 400 by 300, even if its edges seem clearer in the preview.
Noise can become more obvious because the filter does not know which small variations are meaningful detail and which are unwanted grain. A noisy night photo may therefore look rougher after sharpening.
Avoid repeated passes by accident
Processing an already sharpened download again adds another operation to the pixels. Return to the original when comparing the tool's effect rather than stacking copies without a deliberate reason.
For a scan, inspect thin strokes and small lettering. More edge contrast is only useful if those shapes remain readable rather than becoming jagged or surrounded by artefacts.
If the problem is simply that a picture is too small for the destination, resizing it first may change how much softness is visible. Sharpening cannot supply missing source detail.
Keep the version that looks appropriate at final display size. A heavily emphasised edge can look impressive when enlarged and distracting in a normal thumbnail or document preview.