I am sure this method of sharpening has been around ever since electric angle grinders have been in existence. The trick is to sharpen slowly. Don't overheat the blade.
There is another use relating to blades and grinders that is common practice at least in Australia, but I won't mention it here because of the obvious safety issues.
As for welding, just quietly I've seen plenty of weld repairs to blade discs and even blades. I recently got hold of an old mower and try as I might I could not budge the centre nut holding the blade disc to the boss. I ended up using a grinder to cut it off. Half way through grinding I soon found out what the problem was. Somebody must have lost the woodruff key, so they decided to simply spot weld the nut, blade disc and boss to the shaft. Rust had obscured the welds. No wonder I could not budge that nut! LOL!
