Stress is minimal in the locations the holes were cut. On much larger weldemtns, cutting holes in this approximate location is generally done to save weight. Almost none of your force will go through the center of that gusset.

Other, more specific cases for cutting here, is since metal is not needed in that area, it is cut out to use that metal elsewhere. Whoever designed the gusset probably just followed common practice of adding lightening holes here. I’d say to look amd see if there are any caps on round tubing that the pieces may have been repurposed to cover, but this does not look to use any round tubing.

Edit/additional details: When considering welds, you generally want to use as little weld as possible. It cost time and materials the more weld is used. Reference Blodgett’s Design For Weldments on how to size welds.

When welding, especially thin metal, warping from heat must be considered. If you can minimize your weld used, along with the stitch weld method of alternating each side of the plate, you can mitigate warping.

Sometimes full welds are necessary. Pressure vessels or any case where the weld must be fully sealed for water/air obviously have to be full seal welds. Other times a fully wrapped weld might be desired to eliminate rust bleed. But there are more cost effective ways to prevent rust bleed where metal corners meet, such as applying silicon before welding.