If you have beefy objects representing, say, characters, and you only care about their position, you'll use 16 bytes of a 64 byte cache line. So for the "move everything to the right" use case you're wasting 75% of the bandwidth if you go with simple composition or inheritance. If you move from arrays of objects to objects of arrays, your cache utilization improves fourfold. This doesn't matter for your character of, IDK, 20 platforms moving on the screen, but it does matter a lot for entities that are counted in hundreds or thousands. There are only that many cache lines available and memory bandwidth is also limited. If it's your bottleneck, ECS is going to potentially solve some problems. If you're doing something simpler it may not matter at all.