A good definition of interfaces produces a solid architecture which is a good thing by itself. Of course side benefits arrive alone just as being able to build test cases etc.
There is no impact to the actual code, and it opens room for refactoring. The effort to define these interfaces is so low that it doesn't affect release plans. It's all benefits, it seems. I don't have a vote, but I hope that a few words help move the voters :-) Saludos / Regards, José Ramón