What we’ve found is that it’s much more effective for us to brainstorm UI designs when working alongside with someone who can make quality graphic designs.
When you have a mockup that looks exactly like what the final app potentially will be (the “pixel-perfect” mockup), you’re better able to notice flaws and usability issues much earlier in the whole process.
Also, at least for us, it’s much more motivating to have a sweet design worked out first… then turn that into a real app. Moreover, Apple themselves are known to use a method similar to this for their apps and it’s harder to go wrong if you’re following Apple’s lead.
The entire time I was reading this, I couldn’t help but think, “if design is such an important part of your process, you need to own it.”
Tap tap tap deserves credit for seeing the problems created by the physical separation of it’s development and design resources and mitigating them as much as possible. But I’ve been in their shoes before, and to this day I do everything in my power to avoid it.