When I need to adjust a deadline for a multiple tasks I can highlight all of them and move them down the timeline. However, if I have subtasks in those tasks I move the deadlines (for the subtasks) don’t move so I have to manually change the deadlines for those. If I am moving a task deadline I need the subtask deadlines to move as well.
Hey @gabrielle.shallahame, welcome to the Community Forum 
Thanks so much for your feedback on this and for providing us with extra information on how this change would improve your Asana experience!