[David]

If you want to remove them, you can measure the horizontal brace's (purlin) vertical distance to a ceiling joist. Then remove the diagonal brace and check how much the purlin sagged. If 1/16" or less, not much load on it. If more, you should replace the brace where it was or with another brace that provides similar support. I have removed them but I replace with some other brace that doesn't interfere with what I'm trying to do.