Business rules were introduced with Dynamics CRM 2013 to assist Power users in creating validation rules without any coding skills. As such, this is a very powerful feature that's been added to the system customizer's toolbox.
Lots of customizations include various validation rules. From field-level validation to showing or hiding form fields based on values selected in other fields, business rules allow Power users to implement a variety of rules in a pseudocode format. No code is required as the whole creation of business rules is wizard-based.
While this is a step in the right direction, business rules will not replace JScript completely. For complex validations and the implementation of complicated rules, you will find that certain limitations will still require a JScript developer to be involved.
The main difference between workflows and business rules is the location where the process runs. Business rules are primarily meant as client-side logic, and...