Disadvantages: you have to protect the processor from rain, can't lay your head back in a chair with the processor on, a little feedback sometimes but that's no biggie.
While I definitely have to take my processor off when it rains heavily (don't want to fry the battery

) I usually leave it attached when it's only "misting" outside. I just reach up my hand and cup it around my processor, especially if I'm just running into a store or something. Saves me from detaching and then reattaching it.
I also don't get feedback (aka squealing) when I lay my head back in a chair. It happens to others I've heard, but has never happened to me.
With my BP100 (aka BP3) I can reach up and touch my processor when it's on my head and I don't get any kind of squealing or feedback.
This might be due to my settings, but I'm not sure.
Jan