Yes forums and YouTube are great and you should ingest all of that sort of material you can find. Not only do they inform but they encourage. Written by ordinary folk they (usually) have no axe to grind and are forthright and honest based on actual experience.
On the other hand, books are written by diligent well researched people, error checked and impressed a publisher of such expert material that it was worthy of the time and material to print.
Anyone can say anything on a forum.
And usually do.
Books also require no power, Wi-Fi connection, cell signal or batteries. When all else has failed in the middle of nowhere, a book will still function.
They can also double as toilet paper or fire starting material.
Tucked away in a corner of our trailer are two RV repair books and two dutch oven recipe books. The recipe books get more use!