Definition
LZ4 compresses data in independent chunks. Each chunk is a short run of literal bytes and matches against recent bytes, with very little extra encoding. The ratio stays modest, so a file is larger than the same data in LZMA, and decompression is extremely fast. The loader can unpack one chunk and leave the others packed.
Relevance
LZ4 keeps loading fast for bundles that already live on the device. Each chunk decompresses on its own, so the game can load one scene without unpacking the rest of the bundle.
Example
A local AssetBundle of level scenes is built with chunk-based LZ4. Opening one scene decompresses that scene's chunks only. The other scenes stay compressed until the game asks for them.