The main disadvantage is that weak Digital signals will not work. Those who use an atenna and get poor reception will have no usable TV signal at all when things go digital.
Digital is 0's and 1's. A weak analog signal will look crystal clear in digital. If you can't see the picture but hear the sound in analog, you won't get anything but a black screen in digital. There is no gray area with regards to digital. It's either there, or it isn't.
I have exactly that problem in Pocatello. My ATSC converter box does a fine job on DTV-23 (channel 6 analog, channel 10 plus subchannels). There are two other channels that work OK. The rest are unusable. The one usable channel is fortunately NBC. I can watch ER and the Olympics. It doesn't matter that the other ones aren't providing usable signal because they are providing no content that I wish to view.