

Quality won’t increase relative to official methods because it’s already more or less at parity with them. If the file you watch is tagged as a WEB-DL, in most cases it’s identical to the file you’d be streaming via official methods in terms of quality. It’s just remuxed into an open container format like .mkv (the video and audio streams are losslessly copied into a file format which can be shared)
Kinda sorta required if you want to stream assets from storage, an approach taken by many modern games. Might not be absolutely necessary depending on your setup / game settings. BG3 also said SSD required but there’s a “Slow HDD Mode” in the settings anyway, which I believe just shifts more of the streaming burden to RAM/VRAM. If you played on a HDD without enabling it, I guess you’d expect to see inconsistent pop-in as individual assets try to stream in faster than your storage can read. But playing with it enabled might also cause performance drop if your RAM/VRAM was already close to full utilization with the setting disabled