Not real important on a plain steel piece, but for the technical info I offer this tidbit I learned when I was taking aviation technology classes way back when.
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The proper installation of Washers:
The rounded edge, or more precicely the side the stamping die strikes, is the side that should go up.
Reasons? When bolting down something more suceptible to fretting or compression induced intergranular corrosion (mostly aluminum), the sharp edges are slightly lower than the body of the washer & cause a increased pressure area at that point. It can actualy cause or accelerate the corrosion process.
On finished parts, either chromed, coated, or painted, it will cut into the finish. So, if you would like the clean stamped side up it's a good idea to use stainless washers & work the sharp side with a file or lightly with a bench grinder.
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Nerd hat off, thank you, & good night. :P
(than you mr. science for that informative lecture,...)