Regional business development manager is one of those overly long and overly vague job titles that really refer to lots and lots of different tasks and roles. The nature of the job will depend a lot on the industry that is being developed.
The company structure will also matter. If you are the sole manager you will likely have more responsibilities than at a large corporation that has an army of middle managers working very discreet jobs.
But don't let the vague title fool you. This kind of work is not boring or easy or pointless. Middle managers like this are crucial for any organization to grow and operate efficiently. They are a crucial part of the chain of command