Every musician plays a set of instruments, and almost always, one has a major—that is, main—instrument. For example, my major instrument is the piano.
During our period learning to play an instrument (be that major or minor), we would often listen to performances of expert musicians playing the instrument. This is, of course, to get the feel of whatever is possible with the instrument (it’s very hard to play Bach inventions using a jazz drum set, isn’t it?), the sound qualities the instrument can produce, the various playing styles, the roles the musicians of that instrument take, and others.
And then, we would also learn to play with the instrument in an ensemble setting. This is to know the possible roles we can fulfill. For examples, a drummer would be an excellent fit to the rhythm section. A violinist would be very good in melodies. A pianist can take various roles as needed.
Now, as I mentioned before, we listen to performance of expert musicians playing our instrument. But what about other instruments that we don’t play? I think that is just as important. Let me say why.
First, it enables us to learn to understand the sound colours of other instruments. We have got many kinds of instruments. Plucked, blown, beaten, you name it. Even in the same instrument class, you can hear differences, e.g. guitar versus oud. Knowing the different instruments is an enriching experience.
Next, we can learn to understand what roles they can take. By listening, you can identify whether they are suitable for melodies, or harmonies, or rhythms, or whether they are hybrid in this aspect.
Now, this is my favourite: to imitate their styles into our instruments. I listened to saxophones and guitars a lot when I was a teenager. That made me wonder how to play sliding notes on the piano. So, is it really possible? Well, close. Not sliding in the same sense, but there is at least the sense of gradually (with less granularity) moving from one pitch to another pitch.
Also, if later you need to serve in a band, possibly to arrange pieces to make use of those instruments. You know, sometimes you hear people say, “This is a guitar piece”, “This is a vocal piece”, etc. In reality, you can’t really prevent someone else playing your flute concerto with something other than a flute.
Those are just what I can think off. If you have any others, feel free to comment.