I have wondered this too! My situation I think is a little different than others because my background is in graphic design, so a lot of the work in my portfolio reflects that, but I’m applying for studio art programs. My instinct is that ultimately it’s like anything else.. you want to find a program that fits for you. A portfolio with variety will probably be attractive to a program that encourages exploration across mediums. I didn’t even bother applying to places that seemed like they wanted applicants very committed to one medium, but after reading this forum I’m actually wondering if that was a mistake and there was more flexibility than I realized! I’ve seen a lot of people saying they applied for disciplines that are different than what their portfolio shows.