I recently heard an American presenter using the phrase "discover what it is that is important to you."
What is the linguistic difference between saying "what it is that is," rather than "what is"?
The what it is that is phrasing implies that we've already established that "it" exists and now we want to determine its nature. The what is phrasing leaves open the possibility that "it" equals nothing.
...Or it could just be a case of the presenter using more words than absolutely necessary, either on purpose (because he thinks it makes him sound smarter), or as subconscious verbal filler as he tries to gather his thoughts.
They mean the same thing.
In spoken English, the longer phrase could have the implication of focusing in more tightly on what, exactly is the problem; and the shorter one could be slightly more general--but this would be based on context and emphasis.