Need help figuring out the flatten function for sheet metal.

So, I commonly use 1mm thick sheet metal (CRS if that matters), and I need to figure out how to properly use the flatten function.  So, what I am wondering is what the smallest bend is that I can use for an edge flange?  It would just be for a very basic bend.  Is there a definite answer?  Or does it all depend on something that I am not accounting for?

Thanks everyone!

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