Originally Posted by Motormouth

This is an incorrect explanation.

What you are describing (I am guessing, judging on your use of 'added dimension'), is called ''chamfering" and it differs from simply cutting holes in the metal in that a specific chamfer tool/machine is used after the hole is cut to bevel the edge, which is what gives the hole structural strength, often times greater than the raw sheet metal.

The only time basic holes are cut into sheet metal and left that way is when the piece is non-structurally important, non-load bearing. So yes, adding holes to an already un-boxed rear cross brace will be noticeable. Therefore, the smaller, the better.

notice every hole is chamfered (this piece is a structural gusset):


And the weight he would save from drilling two holes in the rear brace would be akin to not driving with socks on; useless.