I'd like to know how the readers benefit from reading. Someone like Grover Gardner or David Timson - these guys ready pretty substantial books - Herodotus, Shel

I'd like to know how the readers benefit from reading. Someone like Grover Gardner or David Timson - these guys ready pretty substantial books - Herodotus, Shelby Foote, Boswell, Gibbon... Do they retain all that they read? Is it an enriching experience?