Outside controlled airspace nobody *wants* to talk to *you*
There are limits to this though. e.g. if you're trainsiting over someones ATZ at 2200 feet technically you're 'outside controlled airspace' but it would be rather daft not to give them a call.
Equally switching the radio off when flying around busy airspace (while perfectly legal) would be an odd thing to do in my opinion. You presumably want to be as safe as possible, and maintain as good a situtional awareness as possible and the radio (and the attendant traffic service/basic service) is a vital tool for doing this.