I know that a major chord is built using the root, a third, and a fifth and that the root note is always the note with the lowest frequency.
So in a guitar, a C major chord would have the notes C(3rd fret on the A string), E(2nd fret on the D string) and an open G string.
My question is why do we play the higher octave C (1st fret on B string) and open E string?
As the C major chord is a triad, shouldn't we be playing only 3 notes at a time and mute the B and high E string like how we mute the low E string? If I include the higher octave C and E, wouldn't it change things? Because clearly just plucking the 3 strings to play C E G and strumming all the 5 strings have two different sounds.
And even if we do play 2 different notes that are an octave apart in the same chord, would the chord be renamed as and add8 or add10?