World::entities is a vector of pointers, those pointers could be scattered in memory. Iterating over them might result in poor usage of CPU caches.

I tried changing std::vector<Entity*> entities; to std::vector<Entity> entities; but other problems arose. (Namely some systems might keep a pointer to a specific entity, the pointer becomes a dangling pointer when adding/removing items to the vector invalidates them)

I think my own inexperience with CPP is showing here, I'll revisit this when I feel more comfortable with it