I haven't worked with XDCAM before. I have a bunch of footage shot on an EX1 - brought it into FCP 6... did not convert to ProRes. I saw in another forum thread that it was recommended to keep it in XDCAM but to set preferences to render to ProRes - why is that?
Because XDCAM is very lossy - you wouldn't really want lossy renders, particularly when it comes to graphics and text. By switching to ProRes you're giving it a codec optimized for post production - it's not uncompressed, but it doesn't have the demands of uncompressed.