I recall Lardy stating in the "Total Retriever Marking" tapes that streamers were only put on the marks to make them more visible to the camera. Recently in a RJ article he advocated the use of streamers, in part, for teaching marking concepts. A number of trainers that I know are using streamers more frequently. So, it got me curious as to how widespread a practice it is and what the pros & cons might be. I personally use them most of the time.