Here's the history as I pretend to understand it.
After effects 7 had gamma problems when rendering out to Apple Uncompressed (AUc) (8or 10bit yuv). Even though the Decklink newly supported AUc they didn't totally scrap the BM codec because it handled Gamma properly rendering out of AE7. This was a lifesaver at the time but the AE to AUc Gamma problems were (kinda) fixed in AE CS3. But the Decklink installer replaced AUc as an option to render out of AE, therefore we must check the "Use Legacy Gamma" in the project settings.
It seems to me it's time to get the BM codecs out of my AE CS3 render output. This is keeping my from using multi machine renders since a project can only have one color settings but the Decklink computers default to BM & my gammas shift. It's also easy in a house with multiple Decklinks & Ajas for the wrong settings to get rendered.