
For want of a nail the shoe was lost;
For want of a shoe the horse was lost;
For want of a horse the battle was lost;
For the failure of battle the kingdom was lost—
All for the want of a horse-shoe nail.
Little things matter. Sometimes little things matter a great deal. Adding required fields helps prevent little bits of data from being lost on the great battlefield of D365.
Personalize Required Fields
In Platform Update 10.0.12. Require has been added as an option to the personalization toolbar.

As long-time readers will remember, the personalization toolbar can be accessed through the option tab, or by pressing the Ctrl+Shift+P hotkey. Once open, the user clicks on Require, then clicks on the fields to be required, and then closes the personalization toolbar.

Saved Views
As Saved views, these personalizations can be published to the desired members of the organization through security roles (see Publish saved views link below in additional reading for more details).
In addition to being a no-development solution, an advantage to this approach is that different fields can be required from different users. Imagine a business process where a general projects team create new projects across the company, but project managers are expected to enter a projected start and end date for visibility once they are specifically assigned to and begin maintaining their project.
Requiring the field through a saved view makes it easy for the project team to create and update other elements of the project through a standard view, while the Project manager’s view requires these data points to be entered.

Project manager view requires project start / end dates

Error message for Project manager not entering required fields

With fields populated, happy projects are all the same.