Lossy compression usually reduces the quality of a file. During the process of compression, the algorithm scans for unnecessary files and tosses them out. Lossy compression is employed when the quality of data is not of necessity, and the file is excess and can actually afford to lose some of its data. This kind of compression has its usefulness in that it saves some space.
In a situation whereby space is not an issue, Lossy compression may not be necessary. Lossless compression is the opposite of Lossy compression, which is used in a situation whereby there is an emphasis on the quality of the file. Higher quality of files simply implies a larger size of the file.
Photographers prefer using the lossless compression as many of them use RAW images, which represents a form of lossless compression for images. These heavy files are really perfect for fine-tuning and editing in picture editing apps such as Photoshop.