You may be able to write a simple command-line application, a utility, or perhaps even a simple desktop application without formally defining your application architecture. But enterprise applications must start with architecture, as there are many moving parts, systems, and enterprise constraints. The job of an enterprise architect is to align business goals and objectives with an IT strategy. And this doesn't only mean implementing functional capabilities, business logic, or a user interface. Enterprise architects are also concerned with non-functional business goals, such as reducing business cost and minimizing risks. Besides implementing business capabilities, application architects are also responsible for implementing the governing policies defined by the enterprise architects.
For architecture, you can use transactions to minimize data loss or to ensure data integrity, or you can scale your application to accommodate higher number of users or business transactions...