All of the information that is found in handmade hero can also be found in tutorials written in the early 2000's and Microsoft documentation, man pages, khronos documentation, etc. It's useful if you have no background and you like to learn about stuff by watching someone program. If you want to read stuff then just read specifications, documentation. By the time I had heard about handmade hero I was at a point where it wasn't useful to me anymore. It's far more efficient to understand and query from the resources that Handmade Hero is based on than to let someone digest it and then regurgitate it over an hour long video. But it's not as easy as watching Handmade Hero.
Its true that there are things that documentation doesn't tell you, and HH probably imparts some kind of living knowledge about the topic, on some level, that hasn't been written down in detail or in a very searchable way. That's probably the most useful part of it.
I haven't watched a whole lot of HH so this is a kind of superficial opinion about it. But I think it's useful.