In my former rock band, one male singer only, everyone was asking me why he has is head always looking down at the floor....Because, even after singing the songs for years, he has never made the effort to learn songs and then, he's reading the lyrics.
With me, as a band leader in my new band, only one type of Members must avoid to read, because they are the focus of the show, they make the show, and they are the singers!!!!
Is Madonna's reading her lyrics? Are any Pop rock singers reading their lyrics and then, are stuck to one place while they are supposed to dance and moove and interact with the public?
The rest? If you have a set of 12 songs only, one hour, well, maybe you could know everything by Heart but even that, a chart for the musicians is like a little cheat sheet for all the special stuff the singer has asked them to do, not too slow, here, give the clue, there, singer what's the bass to do this etc... Especially if the singer is the band leader.
So, recap for me, musicians who support the show, when they have 50 songs minimum for 3 or 4 hours of show, yes, they could have a book or an iPad?
But singers, no way, you learnt poetry by heart when you were little, learn your damn lyric too, it's part of your job!!! But other than them, of course you could have charts...With charts, I can play a show of any number of songs immediately with no practice at 95% within mistakes, the 5% are when the band changed a bit the song compared to the original and this, I have to know it, but the rest, Charts...
After a while, I don't even look at them anymore, only to check which changes I have to do on the keys for programs, even if they are all programmed by Midi, it's better to have your programs in your head:
Imagine starting "Jump" with a patch of symphonic strings?
For horns, if it's a jazz show, they would have a music stand/desk, with the name of the band in it and it's perfect, all big bands have that.
If they don't have that many songs to learn, in rock guitar driven band, they could learn them, if they are in a show with songs ala Bruno Mars, when they are supposed to "be one" with the singers on specific songs, they have to learn them as well, the rest, "pupitre" is ok, they will have the charts in front of them and no one will notice...
But for singers, you are the center of the show, so, do your part, learn the lyrics!!!