I've noticed squeaking of guitar strings in the songs of some of the artists I listened to, and had thought it was a mistake (and very odd that it made its way into the studio recordings) but recently listening to one track (only 15 seconds are needed to be listened to) it seems like it has to be intentional for the amount it's used, also the performer seems to vary between periods of squeaking and not squeaking.
Why do performers squeak the strings/what is supposed to be accomplished by this? Is this a widely held practice? Where did it originate?