Splitting things this way is also handy because you can avoid branches, rather than one big loop with lots of conditional branching you have many loops one for each set of elements represented by a branch. Except rather than having to untangle and manage that yourself the granular systems approach make it a more natural way to implement things.

Although probably once you're at that stage of optimizing gameplay code it's also probably time to write something specific for the problem rather than trying to fit it into a general purpose framework.