Task preview is enabled or disabled under what conditions when doing group assig

Task preview is enabled or disabled under what conditions when doing group assignment ?

As per documentation at forum.appian.com/.../Tasks.html

" Depending on the design, some tasks do not open in preview mode and when you click on the task, you are prompted to accept it before being able to view the task form. Click Yes to accept it and view the task form. "

What is that design & some tasks which does not open in preview mode.
Few findings :
Task form designed using Form designer does not have a preview mode enabled while sail form opens with preview mode enabled when doing group assignment

Appreciate your help !

OriginalPostID-149772

OriginalPostID-149772