It is not necessary to be able to read music in order to play music, any more than it is necessary to able to read text in order to speak fluently. However, if you want to be able to communicate music then being able to read and write it down is a useful skill, just as writing down language helps to communicate.

Being able to read music doesn't make you a better musician, but it may help you to become a better musician, as it will help you to study music. Sometimes being able to see something written down will help you to understand something you can hear but can't make sense of.

On the other hand, musicians who can't read are probably better at playing by ear and probably better at remembering tunes.

I can read music, in the sense that I know what the blobs mean. What I can't do is translate that into sound. For example, I know that a blob on a particular line is "B", but I can't summon up the sound of "B" in my head. Because I learned my instruments by ear, I don't know where to find B on them either - at least not without counting up the scale from a key note, which is too slow to be of any practical use. I keep telling myself I should make the effort to learn where all the notes are, but I really can't be arsed.

I find myself in the position of someone who can recognise some characters in a language like Chinese, for example, without being able to speak it. I know that a set of squiggles means "fish" but I've no idea how to say it.