When saved to disk, images can require a large amount of storage space. Compression is a technique that reduces this large disk space requirement. The more compression is applied when saving images, the lower the disk space requirement.
However, an inverse relationship can exist between compression and image quality. When you use a lossy compression type (such as JPEG), image quality decreases as compression increases.
Accordingly, you must exercise caution and use the compression setting that satisfies your requirements.