http://www.peachpit.com/articles/article.aspx?p=1709190&seqNum=2
so
"
Dynamic Range. Some vendors try to equate bit depth with dynamic range. This is largely a marketing ploy, because although there
is a relationship between bit depth and dynamic range, it’s an indirect one."
this is bit depth
"if an 8-bit channel consists of 256 levels, a 10-bit channel consists of 1,024 levels, and a 12-bit channel consists of 4,096 levels"
so more bit depth is not more dynamic range it's just more points along the RGB Chanel that are recorded, dynamic range is limited by sensor and all the back end stuff, bit depth 8v10 is just instead of 256 levels in each RGB channel you get 1024 now the range that your levels actually cover can be a tiny or a massive dynamic range.
and to add more fun the color space will dictate the colors that can be recorded
this all changes a tad if you shoot raw video/stills but not by much.
working with compressed video is like working working with compressed stills jpegs/h264 are a pain and you cant push them far (good) tiff/prores have more room to play around but not massive and RAW video/still just let you have fun
now to be fair if your working in h264 10bit may let you play around more with how far you can grade as the shadows are not as lossey as in 8bit & you may not get broken gradients so soon when grading but it's no comparison to prores or RAW
also explained here nice and clear
https://photography.tutsplus.com/articles/bit-depth-explained-in-depth--photo-8514
look at the close up with sky in
"A close-up look at the sky shows the posterisation effect. Working with a 16 bit TIFF file would have eliminated, or at least minimised, the banding effect."
ps
http://www.dvxuser.com/V6/showthread.php?358287-HDR-holy-confusion-What-did-I-miss
see AndreeOnline's post