If you are an artist performing at a music festival, or any club gig for that matter, playing a Youtube rip is just foolish. Sure tons of people around the world rip music from the internet, but DJs are held to a higher standard as having music in a high quality format is of the utmost importance for the crowd to experience.
A situation occurred over the weekend at Tomorrowland Brazil when an artist by the name of ALOK played a rip of deadmau5's 'Imaginary Friends' while performing at the main stage. It has been deduced that the track must have been a rip because deadmau5 has stated he never sent out a demo and the track has yet to be released.
We advise all those aspiring to be DJs to be aware of how music sounds on a sound system and that the music will not translate properly if the track is of low quality. Know your music.