Song Choices

I'd like to know what everyone thinks when an Artist goes through the Blind Auditions and they use a Song from One of the Coaches? I know Niall Horan was very supportive of the Artist on Season 28 who sang one of Niall's song for the Blind Auditions and Niall turned his chair for him and he even sang with the Artist on stage... I've also noticed that some of the Coaches have a problem with an Artist coming on the Show and sings a song from one of the Coaches and the Coach doesn't turn his or her chair.