Today we regularly encounter a significant number of applications that don't meet the essential needs of a business or end-user expectations.
One of the reasons for this is that in many cases, interaction designers are not involved and the process of application creation is solely the responsibility of a developer.
This is not always a good idea and leads to user frustrations, bad experiences and - due to hindered productivity - even a loss of profit.
There are significant differences between the old-school static desktop UI design and modern web/mobile application design with all types of interactive content and advanced mechanisms for a powerful user experience.
The differences are even bigger if you are implementing a general UI or business Web application. Not to mention the evolving and growing demand for building (business) mobile applications with all its advantages and limitations.