There are some things worth doing the napkin math first before even bothering writing the code. That includes cache efficiency. Finding and fixing design mistak

There are some things worth doing the napkin math first before even bothering writing the code. That includes cache efficiency. Finding and fixing design mistakes long after you've written a few thousand lines of heavily depended on code is rather difficult to tear out when you realize the design was wrong to begin with. Since it's mostly game engine programmers presently driving this design philosophy imagine a scene in a game. There are some number of entities in the scene. Is that number infinite? No. Do each of those entities exist in their own bubble? No. You want to process all of the entities that need updates all at once. One transformation. You also know that from frame to frame there may be 0 - N entities in the scene but you don't want to be constantly allocating, deallocating, and resizing data structures. So you sketch out a reasonable number of entities to support in a scene. You know the data each entity needs to track to participate in the scene and you figure the best way to pack all of that into a struct of arrays so that processing that update is fast and doesn't waste a byte of cache. You haven't even written a line of code yet. There is a give and take. You have to test out your assumptions and not be afraid to throw away bad code and start again. Once you start down a path you may find that the statistically significant number of accesses for entity data happens for the members related to the physics update. You might choose a different structure to pack that data into apart from the cold data that doesn't change much. Much of data-oriented design is like this: save the modelling for documentation and diagrams and things that humans understand. Write the code for the machine since the machine is the platform. You lose mechanical sympathy when you start designing data structures based on intuition. It doesn't cost you anything to think about these things. It's just engineering.