Why UX & UI ?
At this point you might be wondering about the reason why shouldn't you just begin with the development process. Why invest so much time and resources on designing the experience and interface design in the first place? Well, having a complete human-computer interface (HCI) design makes sure that your customers feel right at home and instead of making countless revisions on the development stage in the after-release feedback, why not perfect everything from the very beginning?
It is like having a strong basement to build your house.
Furthermore, your developers would really appreciate it when they will have a solid reference and concept to work on; and they will be able to focus on what is need to be done, by them. Hence, UX & UI.