Notes on Photoshop and Illustrator:

Scaling or resizing image in Photoshop is "destructive".

When you scale an image small in Photoshop - pixel information is lost or discarded. If you try to scale up an image, Photoshop will have to add pixel information to the image and interpolate the colors and pixels needed, resulting in fuzzy or jagged image.

Scaling in Illustrator is not destructive because the image is vectored based. You can scale up or down without loss of image quality.