Initially I just thought it would be a cool feature to have, like all the other ones here. Flash is more of a load on people's systems than HTML5 video, for example threads like 'what music are you listening to' might crash or slow down some people's computers.
This incompatible mod would've also allowed video embeds from other places than youtube(and new file formats), but I suppose embedding is not crucial, you can still normally link to other non-youtube videos.
But now I'm aware that HTML5 video formats also have less of a strain on bandwidth, and there is mobile support (again, the load issue would benefit from HTML > Flash). Only .ogg video is supported in
the 3.8.4. mod so I suppose it has limited utility.