Explain use of pre_tasks

Book version: 1.21 Chapter 4 introduces pre_tasks (page 63) with a brief explanation that they’re run before the main set of tasks. It’s not clear (at this point in the book anyway) how that’s any different to just adding a task at the beginning of the tasks section. Assuming the reasoning is covered later in the book, it would be useful to reference that section, or provide a simple explanation at this point of the book.

[geerlingguy]

@gaddman - Good point; if you don’t know the context (especially how roles are run prior to tasks) it might seem arbitrary. I’ve made the line read this way to hopefully clear that up:

Ansible lets you run tasks before or after the main tasks (defined in tasks:) or roles (defined in roles:—we’ll get to roles later) using pre_tasks and post_tasks, respectively.

[ssbarnea]

Nobody is removing them, but they do not scale, and for sake of having two ways of writing code, I am inclined to discourage their use. The net is full of users confused about where to stick tasks between roles. Even if I succeed introducing a lint rule for that, it will be optional, so anyone could bypass it.