Like dependency injection is something that a lot of juniors struggle to understand. Or in larger applications DDD and all the crap that goes along with it.
* Interfaces(particularly in java) that have 1 implementation.
* Interfaces with many implementations but where each implementation is used in exactly 1 place.
* large inheritance hierarchies with generic type parameters. I'm sure there's a good use case for this but it's usually a pain.
* Writing "generic" code in an effort to make something re-usable when in reality the code has knowledge of every location it is used in and tightly couples all implementations
With an interface I know that only that method can be called. If a class is passed in i have no idea what methods going to be used. It also gives me a better feeling that the coder has in mind what they need a parameter to do without worrying that they are going to rely on a couple of othogonal methods to be called.