Compression vs. Image Quality
Although storage space, primarily in the form of memory cards, is becoming less expensive, there are still advantages in being able to compress the data for a photograph, provided that the image is not noticeably degraded. The key word here is “noticeably.”
The raison d’être for JPEG in the camera’s menu is that it is both a compression method and a file format, and this is usually the format to choose when it is important to squeeze the maximum number of images onto a memory card. In addition, the recording time will usually be less than it is for a Raw file, and so the images will move through the frame buffer more quickly—all good for shooting large numbers of images continuously.
Compressing a Raw image is a ...