In previous version that was Yes by default, but in any version before it was No by default...
This is like example you have two templates. And In in both templates you have {-Variable.Test-} but in one template default value you have test1 but in second template you default value is test2.
If you will have YES then after copying any action with this variable other template will copy ( replace ) default value also, if no then value will not be replaced ( copied ).