John Routledge has nailed it perfectly.

The only thing that can be added is that some crutches are worse than others.    Rise Up Singing--which you in the UK can count yourselves lucky to be spared--is the allltime worst.   

And for exactly the reason he cited:    it makes it easy to avoid any preparation at all--especially for groups which have a lot of that particular tome.

So you can have the edifying spectacle of a whole group plowing through every verse printed in the book--though they have never seen some of them.    To a tune they also don't know.

RUS--like other crutches--is fine.   At home.    Not at open sings or singarounds.