It sounds like a very technical idea, but basic harmonic analysis just means understanding how a chord is related to the key and to the other chords in a piece of music. This can be such useful information that you will find many musicians who have not studied much music theory, and even some who don't read music, but who can tell you what the I ("one") or the V ("five") chord are in a certain key.
Why is it useful to know how chords are related?
- Many Form (for example, a "twelve bar blues") follow very specific chord progressions (Chords), which are often discussed in terms of harmonic relationships.
- If you understand chord relationships, you can Transposition: Changing Keys any chord progression you know to any Minor Keys and Scales you like.
- If you are searching for chords to go with a particular melody (in a particular key), it is very helpful to know what chords are most likely in that key, and how they might be likely to progress from one to another.
- Improvisation requires an understanding of the chord progression.
- Harmonic analysis is also necessary for anyone who wants to be able to compose reasonable chord progressions or to study and understand the music of the great composers.