^^^ that would be true if it was plate material
in this case, its a flare to make the part stiffer after the holes are cut. male and female dies with a centering ring that locates it in the holes before stamping
and when it comes to lightening holes, theres spacing requiremnts for maximum strength. best place to look for info on that is probably home built airplane forums, they would know about proper spacing, proper sizing, and proper bell mouth angle / size