@AbhishekC1725 History classes are basically used to support auditing by capturing changes in rules and cases. For Eg: When you navigate through a case and visit the Audit tab/ Case History tab mostly present under Case Summary (unless modified) would notice various entries depicting what all changes occurred in that case and who performed them at what time. This was possible because your implementation class has History- class as well which captured all these details.  Visit this link if you want to know more about Auditing : Auditing | Pega