timdiggerm said:
Can I get an explanation of the advantages of using these soundtracks over whatever's on their blurays?
I can't vouch for all of them, but I'd say the goal is to get something that more closely resembles the theatrical audio. The problem is, in many of the above cases, the soundtracks are a relatively small problem on the Blu-ray compared to the video (Back to the Future, Alien/s). But, lacking a correction for the video problems, they're the best we can do.