As a BA, I want everyone to have a common understanding of what we’re trying to achieve so we can deliver the right stuff.
This is generally achieved by asking loads of questions, not necessarily caring about all the answers, but using those to ensure everyone has a common understanding. This typically involves business reps, software engineers, design folk (HCD, business architects etc) and testers all working together to solve problems. I’ll be involved right the way through a project, doing whatever I can to maximise the amount of work not done – why build the whizzy expensive system when you can get 80% of the value for 20% of the effort?
Experience of the subject matter is important, but sometimes too much experience can be a bad thing, as bad BAs can rely on that instead of getting the answers from others.