The benefits of taking a UX led approach are well documented. Focusing on what the user needs from the beginning of a project, and involving the user throughout the whole design and development process means:
Increased user satisfaction
by thoroughly understanding what is important to users
Reduced development time and cost
because rapid prototyping allows changes to be made before committing to code
Reduced user support costs
because products are easier to use
More robust products
accessibility and privacy have been considered from the outset