Great example in this blog post from Intercom of why "should designers code" is the dumbest fucking discussion in the history of discussions:
Truly great products are often a combination of two things: a technical breakthrough and a never-before-seen design it enabled. So it’s essential designers understand the possibilities and restraints of the technology they’re working with, before they can properly delve into the design.
You can't design at your best for a material you don't understand.
Do you need to know how to pulp paper to create posters? Of course not. But you need to understand what you're dealing with. Designing for users of computer software is of course no different.
This is a great point as well:
What [great designers] can do is frame the problem for their team, and create a design process to extract the best solutions from that team.
Right on the money.