There are so many music terms out there...and a lot of them are in Italian, so why bother learning them?
1) When you know them, you don't have to look beyond the page to learn a new piece. You know the basic speed (adagio, andante, presto, etc.), the mood (eg. con brio), if it should be loud, soft, in the middle, all of the above. You can see if the harmony is made of blocked or broken chords, arpeggios, etc.
2) It's easier to communicate when everyone is using the same language. Whether in a lesson or rehearsal, it's best if everyone knows the terminology so you can say "the arpeggiated chord in measure 53" and everyone knows where to look and what you're talking about.
3) The symbols on the sheet music represent terms and the concepts the terms describe. Is it more important to know that a quarter note is a called a quarter note or what to do when you see one? I would say it's more important to know what to do when you see one, but you need to know what it is called to be able to communicate about the music.
The point of learning terms is largely to be able to communicate effectively in a musical situation. And really, most music terms are not that hard to understand or to say, so you may as well take the extra step of learning the terms so that you can understand and communicate well in lessons and rehearsals.
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