If designers are so different, what’s the use of having them around? There are two factors to answering this question. First, there is frequently a misconception of what designer does and contributes to a product. The second is an honest question of the value of that contribution.
Let’s deal with the misconception first. A lot of people think that a designer simply makes things look pretty. In fact, questions like this end up in the forums of design studios like 37 Signals:
Designers decide and design the flow, the copy, the structure of the page, the programmers make all of it come to life by plugging it into the backend. All along both parties trade concessions on how to get the feature done as fast possible by grabbing the easiest value.
So stop thinking about designers as artists who work in a different universe of neat graphics and start thinking of them as someone who decides what goes where, which form elements to use, how to split features between screens, what words to use, and how everything fits together in a coherent experience.
I find 37 Signals position on topics to be a bit harsh most of the time, but they are trying to deal with what appears to be an epidemic of misconception. Personally, I don’t think it is all that bad; but I see that it exists.
Designers are problem solvers, critical thinkers, cultural critics, creative solution providers and a skilled mix of artisan and technician.
The requirements that a designer works to are both objective and subjective… It’s the subjective, creative side of design that’s hardest to explain and hardest for most people to understand. The aesthetic side of design relates to fashion, human behaviour, emotion and cultural influences such as the cultural meaning of symbols. 
When it comes to designers and non-designers, there is often a difference in perspective that makes communication, but it doesn’t need to be that way. Designers think differently and that is part of the value that a designer brings to a product.
Design is a strategic tool used to gain market advantage by companies operating at an international level. Their products, their branding, their promotion and their business premises are all designed to maximise customer acceptance of the goods and services they have to offer and to optimise the day to day operation of their business. 
 Design Institute of Australia – What is a Designer?