So slowly learning both electric and acoustic guitar & getting a little confused about playing open chords and barre chords.

For example you can play the G chord with 4 fingers, 3 fingers and 2 fingers. The C open chord can be 3 or even 4 fingers or they substitute the C for Cadd 9.  I have watched plenty of clips and lessons when guitarists alternate the chord shapes depending on the song or even using different fingers and shapes  in the one song. This applies to changing from open to barre chords. For example some will play the open G whilst others play the same song with the Barre G.

So when do you choose what chord shapes to use in a song or doesn't it matter?  Hopefully I have explained this clearly.

Any help appreciated.