As I see it there will only be two (possible) good outcomes from The Wall: Lots of employment during construction and (if it actually works!) a sudden downsurge in payments to human smugglers willing to risk the lives of those they smuggle.

Downside? Wasted money because I doubt it'll actually make a difference. Government project designed to secure a huge area that doesn't involve direct immediate danger to those at the site. IE: Not an airport or train station. Given the odds this will go just as well as the Bridge to Nowhere in Alaska. Quite useful for a very limited few people (construction workers, and those who actually use the airport), but for most a waste of cash.

Challenge: In this case, it would probably push the smugglers away from the cities and roads and other well populated, where there's likely to be a visible guard after construction, but out in the middle of nowhere there will probably always be a way to get over/under the wall. It'll stop the random runners, and provide a modicum of employment, but not much else.

We'll see.