I don't know who's idea is it to make SCVs attackable as they build buildings, then nerf their hp. It doesn't make sense. Protoss can warp in, and leave to mine. Drones get a 50mineral cost reduction. But SCVs, you not only spend not mining but actually be able to be attacked while building.
The idea is novel, but I've only see 1 area where this actually adds to the gameplay - early drone/probe scout harass to slow down building or weaken early economy.
With a little bit of micro, the enemy unit cannot be hit with the extra scv you sent to intercept him (because of the stupid pathfinding, your SCV keeps overshooting as he turns a corner) he can keep hitting the building SCV. He'll hit it once, then do a 90 degree move, hit it again... your 2nd SCV will overshoot and miss his attack, rinse and repeat, you're going to lose an SCV.
What on earth should I be doing right now? Not only does he harass my SCV building a supply, he's harassing the SCV building the rax and my mineral line is deathly low on SCVs because I keep trying to get him out. The only way to realistically stop this is pull off a bunch of SCVs and kill the probe or drone.
As he is harassing, he'll try to hit you up with zerglings and zealots. If you don't have the wall up by then it's pretty much over (since they can also attack the SCV as he is building)
I find it really annoying how you can attack SCVs as they build now. Why did they nerf the SCV health as well? I don't see the point of this gameplay gimmick. The strategy feels incredibly cheesy.