There are multiple independant reasons why the relationship V - I is powerful, but suffice
to say that for both physics reasons and also convention all of classical harmony is based
on this relationship.
One can harmonise a surprising amount of melodies by
saying that each chord must be either
a) the same chord as the previous melody
b) one chord clockwise on the cycle of fifths
c) one chord anticlockwise on
the cycle of fifths
If you allow for certain chords to have their relative
minor/major then apart from occasional exceptions, you have the basis of the whole of
Sorry, it really is that simple.
Edinburgh Recording Studio Windmill Sound