When deciding between business rules and client-side scripts in Model-driven Power Apps, the best practice is to use business rules are much as possible and only resort to writing code when necessary. The following table lists some of the most important reasons you might choose one over the other.
|Business Rules||Client-side scripts|
|Run business logic on load||Run business logic on save|
|Set field values in form||Instantly update fields in form|
|Show / hide fields in form||Fetch related data|