Setting required to yes on the widgets can help prevent useless server roundtrips.
However, when you combine them with microflow validations, the user will not see the microflow validations when a required field is not entered. You could set the the microflow settings to allow the call even with validation errors. But that defeats the purpose of preventing useless roundtrips.
Generally I don't mix and match.
For very basic master tables, required=yes on the widget with some domail model validations will usually suffice.
For more complex entities, I skip widget validations and domain validations and put everything in the microflow. One exception is unique constraints. A bug in the microflow logic could cause duplicate data. As a precaution I add unique constraints as domain model entity validations.