I bought GF's first book in 2000 after seeing it recommended in a broadsheet newspaper, the writer said after using the routines her baby DD woke up singing.
I didn't know what I was doing or how often /much 8 week old DS should have been napping/feeding through the day, everyone I asked like HVs said "as much as he wants dear," which was totally unhelpful. He wasn't sleeping for very long during the day; he seemed hungry all the time but would fall asleep instantly when feeding, to wake as soon as I put him dow and start cycle again. Every day seemed a battle.
Bought the book, it made perfect sense to me, I did what she said (not everything, some things like waking baby up for a feed at 11pm, just didn't work for me) and within a week or so I had a baby who never cried, unless he'd hurt himself, and yes, woke up singing.
Had Dd 18 months later, straight on to the same routine, they both napped for hours at lunchtime up to the age of 3, so I had 2 hours to myself every day in the middle of the day (albeit stuck in the house). Dc3 I also used it but it was second nature by then and didn't really refer to the book, when I did consult it I realised I had cut many corners over the years.
GF was a maternity nanny and wrote a book to help people who couldn't afford the likes of her, and who couldn't get their babies to sleep. Her intended readership was not people whose babies already slept fine, it was for people who were at her wits' end with a baby who wouldn't sleep at night or who they couldn't put down.