They usually like to roll in it to disguise their smell, a throw back to ancient times, they could sneak up better on prey if they didn't smell like dog.
and why do they always wait until you have just given them a bath !!! Our incredibly stupid Springer rolled in fox poo the other day.I've told him if he does it again, it won't be 'free to a good home' it will be 'free to any home'.
After a bath is the most likely time they will do something like that...
Bathing them strips them of their natural scent and often makes them smell a little perfumed! As I understand it, at that point they'll do anything to smell of nature again.