Having been to Ireland, Scotland, England and Wales before I thought myself pretty familiar with stone walls of various kinds. But I don’t believe I’d ever seen, or at least had never made note of, this type of wall construction which is quite common in parts of Northern Ireland.
According to sources on the internet, this type of wall has a number of advantages. They are quick to build (by comparison to other types of stone walls anyway), take less skill, and make the most of rock resources in areas where rocks in fields are harder to come by. They are not as stable as more complicated walls but that is said to be an advantage as well in that animals (and humans) quickly learn it is not a good idea to try and climb over one as it can result in injury from falling rocks.