I think the first, and foremost, thing to think about is that in User Experience Design, the user comes first. In today's Agile world, user feedback has to be iterative in the design process so that wherever you are in the design process, whether that's user research, interviews, task modeling, experience mapping, wire framing, prototyping, or visual design, you involve the user in a feedback loop so that from a best practice standpoint, design is not opinionated, but rather validated!