Right, let's try the rope for size..... 😃😃

Two things.

Firstly:-

Bruce Springsteen.
He plays to 40,000 people at a time - more at one go than many of us play to in a lifetime.
His lyrics scroll up on a monitor in front of him, like the one PFR described up-thread.
I know - I've seen it.

Q: Does that mean The Boss doesn't prepare properly for his shows?
A: Judging by the quality of the music, the pinpoint timing, the interaction between Bruce, his audience and the band, and the incredible energy generated non-stop for over 3-hours by Bruce and his band, I'd say he's one of the best-prepared, best-rehearsed entertainers and musicians around.

Q: Do The Boss's audiences care that he can't remember every word of every line of every one of the 35-or-so songs in his 3-hour set?
A: Judging by their reaction to him, they don't give a damn, my dear.

If it's good enough for The Boss, it's good enough for me. Providing the performer is accustomed to working with a prompt-system, uses it only as an aide-memoire rather than reading the whole show, and is capable of referring to it, when needed, without detracting from his overall performance (can maintain contact with the audience, head up, eye-contact.....all the stuff we know about), it's a valid and perfectly acceptable tool. If it works for the performer, use it.

Secondly (and perhaps more importantly, IMHO):-

Refer to my post of 28 Nov 14. 06:35 AM

Usual disclaimers.....IMHO, IOSBTBDO etc.