Most organizations spend more on maintaining existing software than they do on new software development. So, if agile methods are to be successful, they have to support maintenance as well as original development.
Two key issues:
Are systems that are developed using an agile approach maintainable, given the emphasis in the development process of minimizing formal documentation?
Can agile methods be used effectively for evolving a system in response to customer change requests?
Problems may arise if original development team cannot be maintained.