There seems to be minimum book size that forces inflation in a whole genre of self-help books that genuinely have good advice. I've read books where all of the advice I need is in the end-of-chapter checklists.
On one hand, it's good to err on the side of too-long a book, as it's easier to skip fluff than to seek out more details, illustrations, and alternative phrasings that aren't in the book. On the other hand, it's annoying to have the extra weight in volume in one's book collection.
I was lamenting this exact thing to a friend the other day. Books are just too long for most self-help advice and it ends up being 80% filler.
The worst is when the first three chapters are about how rich/smart/successful you'll become by reading this book! (Except for the first three chapters, of course, because those are just advertisements for the book you already acquired.)
On one hand, it's good to err on the side of too-long a book, as it's easier to skip fluff than to seek out more details, illustrations, and alternative phrasings that aren't in the book. On the other hand, it's annoying to have the extra weight in volume in one's book collection.