Most people find guitar playing relaxing.
The music whether being played or by simply listening to it can reduce one's stress. It also can be a form of expression. During the 70's, some activists used the guitar to create statements and awareness by creating songs that contents the messages and ideas they are fighting for.
Guitar is the rhythm of the music, it serves as the accent and flare to every song. It states the mood and beat and controls the tempo. It can be called the backbone of every song for it is the basis of how a certain song's sound would end up.