On second thought the idea is probably that the user is made responsible for choosing correct permissions. Most of the time the default behavior of autocreating the dir is probably enough. Except that you might want to get rid of the warning. But not always.
Let's consider my case. My playbook contains a bunch of tasks performed under the root account, then a site/app user is created, and there follows another bunch of tasks for the just created user. If all the following tasks are performed under one account, then the user is to be the owner, and permission 0700. If not, you've got to make this directory writable for all involved parties. Or so my understanding is.
The interesting thing is that the warning is not displayed before running root tasks. But that is probably since I connect as root, not connect as one user and switch to another one.