That depends on the purpose they serve. Even the natives have to take some form of exam to test their literacy in English, such as the college entrance exam SAT in the States. As English learners, we should be aware of distinctions among different registers of the language. The vocabulary and writing style on the exam, or others such as literature, are geared more toward the academy compared with the more colloquial conversational speech. In addition, conversations that follow the descriptive rules allow a broader tolerance for some elements in the language than the more strict prescriptive usages in formal writing and speech. In summation, it is equally important to master and become well-versed in both. We may wonder how we should interact when we run into someone that we know in a museum. It could be a casual banter exchanging a few words from each party. Or it could be a lengthy discussion if they were academic peers commenting about artifacts, history, etc., in which they might use more precise terms to articulate their thoughts in a more direct, clear, and logical manner. It is our earnest desire to perform competently in any setting that mandates a different set of language skills.

I think this depends on different phase or stage.if you are a student.the english exams are more useful because they want to get higer score. If you are an adult and you are starting woking.i think the useful ways is to practice english course. english as an language it is a tool to be used as communication