For the air duct that feeds a room, what is the difference between installing a damper at the register end and installing a damper close to the main supply duct?
The biggest difference I see is noise. The damper at the register likes to whistle when I have it mostly closed.
Also I personally want to install dampers on my main trunks so I can control air flow to each level, this is where dampers on the lines excel at. Controlling air flow to areas of your house. In the summer I want more airflow upstairs and in the winter I want more flow downstairs. If your system is trunked/branched right, you can do this with only a couple of dampers.