Purpose and Rate of Need for Learning Ushul Fiqh

From the explanation, it is clear that the purpose of placing science of ushul fiqh is to know sharia law in act through the rules and methods so that a mujtahid protected from offense.

Fiqh and Ushul Fiqh have the same purpose: Sharia. However, ushul fiqh has a role to set methods and rules of triggering law, while fiqh to do triggering law through methods and rules designated by ushul fiqh. 

Not being acceptable if an opinion says that the science of ushul fiqh is no longer required because the door of ijtihad was closed, we thought that the door will always be opened until the Day of Judgment, of course with some certain conditions. Islamic scholars who saw that the door of ijtihad was closed is because once they saw the impudence of stupid people towards sharia, they sparked the law by lust and spread it among people with no understanding in ushul fiqh. 

People who do not qualify for ijtihad also require this science. They just have to learn the rules of ushul fiqh to references used by mujtahid as the basis of ijtihad, their madzhab policies, and occasionally they can compare and favor (tarjih) one of legal opinions then trigger a law in appropriate with methods used by imam mujtahid in determining and triggering the law. 

As Shariah law can not escape from this science, lawyers, judges, professors, etc. also can not escape from ushul fiqh in order to decide a law. Because the rules and propositions set by ushul fiqh (such as analogy and its dalil, rules of ushul for interpreting nash, procedures in meaning of words and sentences, supporting evidences and rules for favor [tarjih] among propositions) is one of the requirements should be dominated by people who are competent in deciding a law in order to discover the law and interpretations contained in it. It is the reason why the Faculty of Shariah and Law in Iraq, Syiria, Egypt and other countries still lecture this science to their students.