Command buttons

Yes if you want this command button to be the default; otherwise, No. The default is No.

When a command button is chosen as the default, it is selected when the user presses ENTER or double clicks the mouse. This only applies to the first command that is received after the user opens the form. When the user presses ENTER or ESC, the system first checks to see if there is a specified response. The default property and Cancel Property are only executed if no response occurs.

Reference