Linked from
The 19 pages that link to Lossy compression, each with the reason it gives.
Digital audioRelated: It explains the irreversible information loss in formats such as MP3.
Image compressionRelated: It achieves smaller images by accepting some reconstruction error.
Video codecRelated: Most delivery codecs use lossy compression to reach practical bitrates.
Image file formatRelated: Many image formats trade some fidelity for smaller files.