It can save data by excluding data streams that you don’t need. For instance, I don’t need French, Italian, Japanese, German 5.1 audio streams that each have 700Mbps bitrates or higher, nor do I need an English 1.5Gbps master audio stream, a 700 Mbps English stream, a 500 Mbps descriptive audio for the blind, and 5 different special edition commentary tracks for a film I’ll watch once or twice. All those tracks can really add up, and torrent sites are often country or language specific, so remuxes might have original language and/or native language audio only.