I remember hearing a story about a conductor who was mightily upset. The power went off - but the orchestra carried on playing. They all knew their parts. The music was just the aid memoir.
Trouble is - put up a music stand in a folk club and a few people use it. Then everybody does - and even the experienced players start to sound uninspiring. Too easy to sing a quarter learned song/tune + you are too busy reading the notes to listen for variations others might make. Gone is the creativity.
Its the same with dance calling. Its too easy to just read the calls from a crib sheet. Takes ages to walk through the dance and some calls are not clear even when you do read them. Best to have the dance ' in your head'.
FloraG.