But Business Rules doesn’t only work on forms! If you set the scope to Entity, the business rule run on Server. Which means, you could implement some business logic on server using this instead of Workflow or writing a Plugin!
A few things to note though:
1. Entity scope business rules run on all forms.
2. Entity scope business rules run on form and server. This means if you create or update record using CRM form, the business rule will be executed twice, once on form and once again on server.
3. When using Entity scope, you can’t use circular reference. This limitation protects you from unwanted value changes because it is executed twice.
4. Business rules run when form is loaded or field values changes. They do not run when the entity is saved unless the rule is set at entity level.
Read more about Business Rules from technet https://technet.microsoft.com/library/dn531086.aspx.