The problem with this is that it only works as long as everyone instinctively knows that you don't use all the kitchen-sink stuff. It's there but everyone know

The problem with this is that it only works as long as everyone instinctively knows that you don't use all the kitchen-sink stuff. It's there but everyone knows you don't use it because that way insanity lies. And it works more or less OK until someone comes along who doesn't know that you don't use X, and it's in the standard so your implementation isn't standards-compliant and we'll go with your competitor over there instead because unlike you they do support it. And so, over time, all the crap that "everyone knows" you don't use, gets activated and used. Speaking from experience here, not an invented edge case.