Proper side-part haircut

I have been told two different things by hair stylists I have gone to in the past. I have a middle part and yesterday the stylist parted my hair down the middle. I told her where my part was and she said it was fine she would cut my hair and the layers in and then switch over to my side-part at the end. Which way is right? My hair turned out okay but when I had another stylist do this in the past it left a huge chunk of hair right near my face that was two inches shorter than the rest and when I went to get it fixed by someone else she told me a hair stylist should always cut my hair around my side part. Thank you in advance for any advice.