fer yer theory needs

One question though

Why exactly do we double the chords ?
as in when playing a major chord maybe

we fret 1,3,5,1,3

why is that ?

is it just for the sound ?

i do it basically for the sound

is there any other reason why people play chords like that ?

I'm sorry, I don't quite understand your question.

Are you asking why people double the notes in chords?

In that case, it's usually because on a guitar, it makes them much easier to finger.  A piano player doubles notes far more rarely.

Jazz players who are obsessed with not doubling notes, try to find the leanest possible voicings for chords and prefer not to play any note that other instruments are playing.

For example, if the bass is playing the root note, they leave it out of the chord.  They often avoid the 5th too, to make the chord even sparser and end up playing only the 3rd and 7th.

Strange people, jazzers.

If you are not playing with a band, there is no reason to avoid doubling notes and often it is desirable.  That is why solo guitarist/singers often play 12 strings.  In a rock band, doubling notes is often desirable too for a thicker sound.

Doubling the chords?  You mean doubling the notes?  IF you played a 1-3-5-7 it sounds a bit more bitter than a chord with the root doubled 1-5-1-3-5.  Doubling certain notes of a chord makes it sound different.