It will always fail. If the map's big enough, the other guy will have an extra SCV/Drone/Probe built be the time you get there, and might have enough minerals for building ANOTHER one. And if you try to repair your SCV's, that will cut down on your attack power, as well. If the other guy has even one SCV left, he can mine, build a marine, and take out your 0 mineral, 0 SCV base.

If it's a small map, you still have to actually find where the other base is.. giving the other guy a short amount of time to mine somewhat and build another SCV, if he's fast.

*Exception: The other guy's an idiot. A complete idiot. One who doesn't know what an SCV is.