You can't run Amiga apps on AmigaDE (meaning apps made for the Amiga computer or for Amiga OS). You can only run apps made specifically for AmigaDE/Tao Intent (of which there are very few).
With AmigaDE, you're coding in a supposedly CPU agnostic way so the app will run on any device running AmigaDE.
Advantages? I can't think of any... Theoretically you've got a wider market to sell to, as there are far more PocketPC owners than Amiga owners out there, but in reality sales have been very bad, there are no more than a a couple of dozen (shareware-quality) games available, and there hasn't been any new development on AmigaDE for many months. It's pretty much dead.
On the bright side, the AmigaDE SDK can now be picked up for next to nothing from many dealers. (Yes, we know must companies give away their SDK for free, but this is Amiga Inc we're talking about). In reality, If you want to write PocketPC games, there are far better ways of doing it than AmigaDE.