In my projects as consultant, I still encounter customers that do not consider architecture as part of their project. They start projects with vague requirements and are of the opinion that these requirements will become stable during software construction. In our current webbed society, they also forget that the software has to function in an open environment. It is their opinion that interfaces with other partners in an organization network will become stable at the end.
What they forget is that partners also have to adjust their software to be able to function in the new environment. A software component can only be developed, in case all interfaces are fully specified. IT architecture has several views, e.g. a business and information view. One of the views is: the set of components and their interfaces. Clear, concise and complete specification of those interfaces allows all partners in a network to adjust their software simultaneously. The result will be a fully functioning system, operational within planning and hopefully budget.