There are many different kinds of projects but most of them can be categorised in either customer driven projects or business driven.
In customer driven projects, the investment is judged based on the benefits derived from customer goals. The centre of the project is customer and utmost care is given to the customer needs. In such projects, the requirements from the business can be modified to align with the user stories. The discussions between the stakeholders is also focussed on what customer wants.
As a Business analyst, I have also seen that many customer driven projects are more focussed on the customer experience and hence the requirements are sometimes derived from the customer designs. This means that the customer design is in the driving seat and also might lead to siginficant scope creep based on customer tests.
On the other hand, the business driven projects are judged (read evaluated) based on the benefits derived from business goals. In such projects, the requirements from the business cannot be modified and the discussion is focussed on what business wants. I have noticed that in such projects, tracking requirements to functional specs, to test cases, to user test scripts is very important from a scope perspective.
Although, there is never black and white. All the projects have both customer and business goals. However, for a successful delivery and also from a senior management communication perspective, it is very important to understand the direction of the project before hand. A concious effort should be dedicated to understand as to which goals (customer or business) has more weightage in order to achieve a successful project delivery.