Validation rules versus field-level and layout required
Key Takeaway
Page layout required works only on detail and edit pages. A universally required field must have a value whenever a record is saved. A validation rule uses a formula to express conditions, and it follows the record, not the page.
Salesforce gives app builders several ways to make sure records hold complete, correct data. You can mark a field required on a page layout, make a custom field universally required, or write a validation rule. These options differ in where they are enforced and how much logic they can express, so many exam scenarios come down to choosing the one that fits the condition and covers how the data gets in.
Page layout required
A page layout can make a field visible, read only, or required, but only on detail and edit pages. Marking a field as required on a page layout, known as page layout required, only ensures that users enter a value.
A page layout controls presentation, not data security.
For example, imagine you remove the Edit button from a page layout. That change doesn't stop users from inline editing.
Field-level security overrides less-restrictive page layout settings. If a page layout requires a field that is read only in field-level security, the field stays read only for that user.