a little science always helps the soul and vice versa.
I think the definitive answer is… it depends.
I played trumpet through school, so I can read and write. However, after high school I started playing in rock bands. If you’re talking to a keyboard player no problem, but for the most part it’s a language pop band musicians in general don’t speak. I’ve experienced the same in top 40 bands, etc.
True stury - I played with a drummer who did the road with the 60s one hit wonder Strawberry Alarm Clock (Incense and Peppermints). We’re doing a standard bar cover band thing and he had the beat backwards as we rehearsed a song (My Sharona). I told him he had the snare on 1 and 3 but it needed to be on 2 and 4. He looked at me and said, I quote, “Wow, man. I don’t count that way.”
As others have observed, style heavily influences the likelihood of musical literacy. If you’re playing jazz or scoring a soundtrack, it’s high. If you’re playing AC/DC, not so much. That doesn’t mean that rockers are always musically illiterate, just less likely to interact with written music. I think the important thing is to be able to speak the other person’s language, be it notation or “feel.” Otherwise you simply can’t communicate.
That said, it’s worth mentioning that while not always necessary, the more you know, well, the more you know.
The general smart-aleck answer “I don’t need to know how to read or write” affects the same in grammar as in music:
A. The juvenile use of “then” when it should be “than”, and vice-versa.
B. The use of “quite” when describing a low volume sound or environment.
C. A bass player who can’t transpose, or can only play in certain keys.
D. A guitar player who actually pays someone else to tune his/her guitar.
E. Drum circles.
ROTFLMAO!!! 
Now there is a thought.
Reading drum circles! Yah! 
Now where should that ‘ratamacue’ be played???
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Precisely!
And my original question goes to todays current young musicians.
Can we still say that ‘it depends’ or is it more like driving a stick shift car.
Good to know how to do yes but odds are, you will never have to.
Is it
1-simply a waste of time (today) to learn to speak/write this ‘language’?
or
2-young un’s should learn it anyway; just in case?
I am wondering about the ones that want to do music as a living
and not just a hobby etc.
However in this thread we did hear from Strophoid who is as he posted,
nearly 24 year old; (my daughters age) and thanks so much for yer input and P.O.V…
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Mahalo no ka oi
Sending much Aloha.
no ka oi
Maui ‘IS’ the best!
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