What is the purpose of the "grounding" tab/wire on a 3-prong to 2-prong adapter?
Yes, it's designed as a ground attachment. No, it's not simply to keep it from falling out, as evidenced by the style you haven't shown that provides a pigtail green wire, and the fact that the terminal in question is electrically connected to the ground pin of the receptacle side of the device.



While it is true that this will not always result in a ground, and may (I haven't got time to sift through code, nor code on a computer to sift through) not result in a ground approved by code, it is, nevertheless, what it's there for, and in quite a few cases it does, in fact result in a ground - whether or not you like it.