Answer : Cobblestone walls have better blast resistance and is not flammable, making it a slightly better defense against creepers and TNT, as well as making it usable near lava or fire. Other than that, the difference is purely aesthetic. Today I discovered, aside from the important and most relevant differences mentioned by fredley, cobblestone walls also have noticeably bigger hitboxes while still retaining the taller-than-a-block effect of normal fences, making them useful in certain situations for mob farms and mob elevators. For example, baby zombies, having a square hitbox of 0.3 x 0.3 blocks, can squeeze through the corner gap between a fence and two solid blocks of 6/16 = 0.375 blocks, but cannot squeeze through the gap between a wall and solid block when there is a wall post , since the empty area is a 5/16 x 5/16 block square minus 1/16 x 1/16 in the corner taken up by the post, but can squeeze in the 5/16 x 5/16 block area when there is no post (when there are two b...