*Note: AGC still kicks in when recorded to the camera, so it's not the best audio quality, but still worth having backup, right? and easier way to sync with plugin.
The reason I do this is because I want to sync my audio and video easier while editing by having non-muffled hard-to-see audio level. I use Adobe Premiere Pro, so can't Plural Eyes like Final Cut users. (UPDATED* now Plural Eyes is available for Premiere as well, hoorah~!)
AGC on DSLRs are stills pain in the butt, but better than nothing, right?