Frank Chimero explains why it’s important for designers to know how to code, which seems incredibly obvious. This rung truest:
Design decisions are affected by both the content and the format, like how a sculptor would make different decisions if she were working with clay rather than marble.
You don’t have to be an expert, but you do have to understand how things are built. If you don’t, you’re going to make assumptions that affect the work of everyone else on the team.