I have worked for companies that use the Agile method and for ones that use the "waterfall" method. Agile seems to fit with the reality of the software development process better than other systems. The main advantage of Agile is the expectation of change and the methods for dealing with it. In systems that use a cast in stone pre-defined plan any changes (and I have never seen a project that didn't have changes) can cause problems because the design was inflexible.