You create a model-driven app. You need to add custom business logic to the main form. You consider what to use better for your business requirements: the business rules or client script. 
Please select all the main form operations that need or benefit more from the client script`s implementation.

Answer options:

A.Set field values
B.Referencing related data
C.Running business logic on a form load
D.Instant update of the form fields
E.Show and hide fields
F.Running business logic when you save the record

Correct Answers: B, D and F 
Power Platform provides a variety of tools to extend the platform and user experience. If you need to work with the Dataverse, you can use Dataverse Web API and Organization service. Or develop your business logic by using the Dataverse plug-ins. You can use Data import, Synchronization, Virtual entities, Azure integration, and Webhooks for integration purposes. 
Before you start coding any additions or extensions to the apps, you need to consider the alternatives that Power Platform already provides to save your time and automatically integrate the outputs within the platform. The Dataverse declarative options for the business logic include the use of business rules, Real-time workflows, actions, and Power Automate flows for your business requirements. 
You need to evaluate your business requirements and decide what type of solution you should use: declarative or code. Option B is correct because if you need to use the data from related tables, you need to use a client script or a Web API.
Option D is correct because if you need to update fields based on data changes in a form, it is better to use a client script. After all, the business rule updates data only on the data retrieval during the form load or refresh.
Option F is correct because if you need to run a business logic OnSave you have to use the client script because the business rules run logic on a form load or refresh.
For all other options, the business rules are better out-the-box solutions than client scripts. 
For more information about the use of the declarative or code Power Platform solutions, please visit the below URLs: 

https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/client-scripting
https://docs.microsoft.com/en-us/learn/modules/automate-business-process-flow-client-script-power-platform/2-best-practices
https://docs.microsoft.com/en-us/learn/modules/introduction-power-platform-extensibility-model/4-exercise