I watched it years ago, so going from memory… it’s definitely a bit of a gimmick, but the idea is that if you slice up your steak on your cutting board then the seasoning will transfer to your steak all over - not just top and bottom.

The YouTuber (Adam Ragusea) has acknowledged that it’s a gimmick and he doesn’t prepare his steak this way. Since th video came out several years ago, he’s actually become a really good food science YouTuber (which this video definitely was not).