Summary
The practical difference in Halacha from the debate of R' Eliezer and R' Akiva (Hagaddah Shel Pesach, Mechilta Beshalach 14:31) if each plague consisted of four or five (parts) (If the plagues were just in the four elements or also in potential matter (Kol Bo etc) - in Halacha, to the aspect of the prohibition of Chametz. And the explanation in Avodat HaAdam. (5739)