What are the disadvantages of not following dependency inversion? [closed]

what are the disadvantages of not following dependency inversion?

I know one which testing the classes become easy.is there any other difference other than this?

suppose I have class A and class B. In D.I we create an interface of class B functions and class B implements it in the same way class A uses the interface rather than using the concrete class B.

I know this helps in loose coupling but I don't get what is the disadvantage of it.