When the FASB issues a new Statement, it may require companies to apply the new principle prospectively,

Question:

When the FASB issues a new Statement, it may require companies to apply the new principle prospectively, or to account for the change by the retrospective adjustment method.
Required
Why do you think that the FASB requires one of two different transition methods when a company adopts a newly required accounting principle? Do you agree with the use of two alternative methods?