“Thanks to this mechanism, we can copy 4 bytes for the cost of one byte.”
EGA’s planar memory made shifting pixels sideways expensive, so the developers simply refused to do it. The backdrop moves in 4 pixel steps against the map’s 8, alternating between two precomputed copies. Latch copies made tile drawing about 60 percent faster. That was real engineering on a 286, and modern games ship 100GB patches.