In practice, working with them can be quite different. In a lexically scoped representation (either ANF or CPS) you have to preserve lexical scoping after each

In practice, working with them can be quite different. In a lexically scoped representation (either ANF or CPS) you have to preserve lexical scoping after each transformation, which can be pretty annoying if you want to do optimizations in their full generality. With SSA, you have to preserve dominance, but you don't have to update the dominator tree (the equivalent of the information encoded in the lexical scoping of ANF / CPS) if you don't want to; you can simply recompute it. Of course, the advantage that ANF / CPS have is that they can naturally represent higher-order programs, but for first-order programs they don't really have any advantage over SSA.