Also a player CAN be very creative and spontaneous with a chart. Chart reading does not inhibit "free-style" playing!!!
They certainly can be spontaneous...all the chart acts as is a map.
If you needed directions to a certain place, then, you'd use a map, or have someone draw one for you.
The first time you'd have to look at it a lot.
Next time, not so much.
Eventually you wouldn't need it, and, perhaps, after getting familiar with the territory, you could try other ways of getting there, perhaps a different street with more scenic diversity...or a shortcut.
Then, if you hadn't been to that place in quite a long time, you'd just take out your map, and depending on how long you were away, you'd study it briefly, or intently, but probably, never as much as the first time.
I doubt if I remember, or ever did remember, the changes for 1000 songs...heck, maybe, and that's a big maybe, about a third that many...that's why I have charts and fake books...just too much to remember, on top of remembering which style, what tempo, what instruments featured...even what key, if using transposition.
Someone that can remember 1000 songs and their chords, or lyrics, or both, must have a "photographic" memory.
I've been reading charts and fake music for a long time, and I'm not usually "locked in" to rigorous interpretation, unless it is specified beforehand.
Ian