[zdw]

Mostly that VLC has had noticeable issues with displaying some kinds of subtitles made with Advanced SubStation (especially ones taking up much of the frame, or that pan/zoom), which MPV-based players handle better.

If you want a MPV-based player GUI on macOS, https://github.com/iina/iina is quite good.

[arch1t3cht]

Note that, while I haven't had time to investigate them myself yet, IINA is known to have problems with color spaces (and also uses libmpv, which is quite limited at the moment and does not support mpv's new gpu-next renderer). Nowadays mpv has first-party builds for macOS, which work very well in my opinion, so I'd recommend using those directly.