In MSD 365, when we add sub-grid on form by creating relation between two entities, it will gives Create (+) button and associate view button. When we click on Create (+) button, dynamics shows already created associations between these two entities, ref below screen shots…
Some time we don’t require this associated records and always want to create new record by avoiding all those clicks. We can achieve it by making relation mandetory, just as shown in below image.
…and you are done, now go back to the subgrid and click on the ‘Create’ (+) button, it will launch new create window and won’t ask to select existing association.