C major chord has only 3 notes, right? Why we play more then free of them... so they aren't triads?
Whole neck chords simply repeat the notes at different octaves, or possibly add additional notes in what you call an extended harmony that has more dissonance in it and is used to create interest or perform a certain harmonic/melodic function.
Quote by matiss.gutans
C major chord has only 3 notes, right? Why we play more then free of them... so they aren't triads?

As stated, they're octaves of the notes.

Check it out:

Take an open C Major chord in standard tuning. You'd play it as x32010. Those notes are xCEGCE. See how the C and E are repeated? they also happen to be the 1st and 3rd of the chord which are (arguably) the most important notes in a triad. The 1st denotes the chord, and the 3rd denotes major or minor, but that's a whole other conversation

To understand why we do it, I think it's helpful to look at music in a band context.

Basically, in nearly all forms of western music, we have the Melody and the Harmony which drives the pitch side of the music (there's also the rhythm and beat that drives the other side. We could also get into timbre, but let's not right now).

Your singer (in a rock band context) handles the melody. The guitar and bass handle the harmony (another way to look at harmony is to imagine people singing in harmony. Each string is another dude or dudette's voice singing).

Imagine your singer is singing a C note. You're playing a C Major chord on your guitar, and your Bassist is clunking a C.

The notes go:

Singer: C (higher range) + subtle harmonics unintentionally made by a human voice
You: CEG (lower than singer), CE (In range with singer) + all kinds of subtle harmonics unintentionally made by your guitar.
Bassist: C (even lower) + subtle harmonics unintentionally made by his bass guitar.

So all the notes together amount to one big C Major triad repeated at different octaves with the singer singing a nice cool C. You could even add a low G (332010 or GCEGCE) to your chord to add in another G (you're playing a G/C, but because the bassist is hitting a low C, the overall perceived chord is still C Major)

Pretty boring, but as you can see, guitar chords are harmony. You could certainly JUST play a C Major triad (and this has it's place!), but the more octaves you add, the more interesting (and harmonically rich) sound you get.

Experiment what works best in the context of a song you're playing. Read up on some theory too

I hope I was able to at least somewhat explain what's going on and why we play octaves on top of the triad (and sometimes below).
This guy just doesn't want to learn chords with anything more than a root, maj/minor third and fifth. Ever heard of a dominant 9th chord before? It woud look like C E G Bb D. As you learn, you will discover more advanced harmonies as you go along.
Block chords (normal uninfected triads) are much easier on a piano.

Every interval has a relationship between two notes. First and third, major or minor. The third and fifth and the first and fifth. If you have a normal block chord set up, it will sound a certain way.

So we have one three and five, consisting of three different intervals. Assuming we are major, you have a major third between one and three, a minor third between three and five, and a perfect fifth between one and five.

Now imagine if you took the one and played it one octave higher while still keeping the other notes in the same register. The three would now be the bottom note. Your intervals would change. Between three and one, you now have an interval of a minor sixth. Between three and five, you still have that minor third because we didn't move those notes. And now between five and one, we now have a perfect fourth.

Most music theorists would argue we are still playing the same chord, because all the notes are the same. What we have done by moving the root note to the top of the chord is calls inversion, which is one of many ways to create a different voicing.

In short, we repeat or omit notes in chords because it changes the way the same notes sound together.
Also, you might get a better response posting this question in the music theory threads.

As slayer1979 eluded to, there are chords with more than just three notes in them. You will notice Chord is defined as three or more notes.

Direct quote of the wiki: "A chord, in music, is any harmonic set of three or more notes that is heard as if sounding simultaneously."

mjones1992 already answered your question already and there is nothing else to add. I just thought I'd illuminate what slayer1979 was talking about (in a broader manner.)
Voice-leading, sound, context, melodic function, there's 6 strings on a guitar so why not use them, extended chords etc etc
Quote by matiss.gutans
C major chord has only 3 notes, right? Why we play more then free of them... so they aren't triads?
Boy oh boy, you better stay away from the 12 string. Because every time you play a triad, you get six notes.
Quote by matiss.gutans
C major chord has only 3 notes, right? Why we play more then free of them... so they aren't triads?

It's still a triad because you are only playing C E and G. Repeating notes at different octaves doesn't add different notes, so it stays a triad.

Why play more than one of a C E or G? Because you like how it sounds