As a composer and a piano player i am very confused why do i need to study intervals? I understand it is for ear training but what quality and purpose does it have realy? Is it necessary? I cant see where is benefit? I read this article and it did not satisfy me for some reason.
Learning about intervals gives you more ways to think about music, and it is always good to have many ways to think about hearing, playing, and composing music.
Consider a drop 2 voicing of a major 7th chord in first inversion. This voicing has a distinctive sound, and if you listen you might notice a minor 2nd between the inner voices.
X: 1 K: C L: 1/4 "CMaj7"[EBcg]
Knowing about and being able to hear intervals gives you a way to think about why this voicing sounds different from other voicings of a major 7th chord. After recognizing the minor 2nd in this chord, you might wonder if other chords can be voiced to include minor 2nds; for example, this might inspire you to discover voicings of 7♭9 chords incorporating minor 2nds. Being able to identify a minor 2nd in a chord played by someone else may provide a clue about which voicing they are using. Having found a few places minor 2nds crop up, you might listen to some music which involves minor 2nds to see how they are used there; Thelonious Monk was famous for using minor 2nds in his playing.
By naming intervals and learning to hear them, you can isolate them and think about them more deliberately, but this also makes it easier to communicate with other musicians. For me these are two compelling reasons to learn about intervals, and theory in general: this sort of work facilitates communication and helps you to clarify your own thinking.
One very good reason to be conversant with something is to be able to convey what you are talking about to others in an intelligible way. Knowing the correct terms and understanding what they represent is part of that. Using a common language!
It's also like there are many ways to subtract numbers in maths. Most, if not all, will produce the correct answer, but usually, one person prefers one way. Maybe in your composing, you are happy thinking note names and their relationship with others, but that's not the only way. Do you know the P5 from root in every key? You probably have a method to get there, and the intervals thing is just putting a name to it. If you write C>D#, it'll sound like C>Eb, but one of them is technically right, the other wrong. Do you want people talking about how you can't actually write properly? I seem to do it a fair bit, with notes not written properly because the composer doesn't know or apply intervals correctly.
That sounds like a mini rant, but put another way, would your confidence at the doctor's be changed when you hear him ask for 'that silver pointy thing please, nurse'?
Most people, even if they have absolute pitch, perceive music from the point of view of relative pitch - that is to say, two melodies with the same set of intervals in sequence, but starting on a different note, are actually heard as the 'same' melody:
Do you hear those two melodies as somehow similar? If so, then your hearing also works from the point of view of relative pitch, and the concept of intervals is relevant to you. As Tim says, you might as well 'study' intervals to a sufficient extent that you can use the same vocabulary that most other people use to describe them.
Incidentally, I don't always think in terms of interval names - sometimes I'm more interested in frequency ratios, for example. But knowing the more common terminology doesn't hurt...