This means it is a bit of a mess, and your projects tend to be difficult to construct and, especially, maintain. In particular, if you add code to a Director project, you tend to end up with lots of scripts all over the place, and it can be hard to keep adequate track of which code produces which effects. Of course, this is to some degree a personal matter - some people prefer Director's timeline metaphor.
AMT titles are truly cross-platform.
I have yet to write an AMT project that doesn't transfer to Windows with no problems. AMT has excellent screenhandling built in. You can display 8-bit images using either the Mac system palette or have the system switch palettes on the fly. This works well on both Mac OS and Windows. It allows you to build complex programs quickly and efficiently and support large scale code-resuse.