When you delete a task in Asana, there is a red banner that appears at the top. That banner contains a button that says « Delete permanently ». The problem with this kind of banner is that it does not take into account the fact that many people (including myself sometimes) just don’t read the interface properly. I have seen clients click on that button without even thinking about it every time they deleted a task.
Going into the habit of permanently deleting something is dangerous. Because you never know if you won’t be needing that task one day. Deleting is usually enough unless you really have confidential things you want to hide. Otherwise, just delete the task.
On the topic of deleting tasks, I almost never do. If I don’t need to do something anymore, I usually write a comment explaining why and the context, and I complete the task anyway. That way it is easier to find it again, just in case…