What it is for
So that the technology fits the business processes rather than the other way round. Requirements engineering is the tool for reconciling technology, processes and what people actually need, before a decision is made.
Without that step you procure what was convincing in the demo, and afterwards adapt whatever can be adapted.
How it runs
Systematically, in workshops. We help define and capture every relevant requirement and figure: functional and non-functional, and in particular the numbers that later decide the architecture.
Why it comes first
Because other services build on it. A data management design without known access patterns and retention periods is guesswork, and a disaster recovery design without RPO and RTO is not a design.
Requirements engineering is therefore rarely the project somebody rings about, and often the one the project should have started with.