Mandera Wall will keep out Al-Shabaab Fighters

The Kenya Government has apparently decided to build a wall along the more than 200 km border between Somalia and Kenya, the major purpose of which is control the entry of Somali nationals into Kenya.
The wall is part of a larger strategy to keep out Al-Shabaab fighters in particular and illegal immigrants more generally, and to prevent what some have already termed serious encroachment on Kenyan territory.
The Mandera County government is concerned with crimes committed by Somali nationals who retreat across the border to the border town of Bula Hawa in Somalia and, thus, escape arrest and prosecution by county and national authorities.
The programme reflects a belief that clear demarcation of national boundaries is itself a legitimate government project.
As I write, the project appears not to be a joint Kenya-Somalia effort.
The Kenya wall project brings to mind the other walls that have been constructed by countries around the world for the same general purposes, some of which are still in existence.
The key question, then, is what good are these walls? What purposes do they legitimately and effectively serve? What are their limitations and with what consequences?
A prior question is what good for whom?
Since I am not familiar with Mandera County, I will stipulate that the wall may be useful for the county for deterrence and pursuit of local criminals fleeing across the national border.
The evidence on whether and to what extent, at a macro level between nations, walls like this one serve useful purposes appears to be mixed at best.
Source: Nation.co.ke