What exactly is the purpose of pre_tasks/post_tasks when one can just put "pre" tasks before the main tasks and "post" tasks after the main tasks in the "tasks" directive?
I've read the documentation many times and I can't understand the need for them. I must be missing something here, right?
Primarily they were introduced to provide execution order when using roles:. post_tasks is probably mostly useless. The execution order is:
pre_tasks
roles
tasks
post_tasks
What exactly is the purpose of roles then? 
I mean, is there a difference between roles and use include_role / import_role inside tasks?
roles: existed long before include_role and import_role. Many on the core team would say that import_role and include_role are the future. I personally would like to see pre_tasks, roles, and post_tasks deprecated. Time will tell…
So, in other words, with include_role, import_role, and tasks, one can do pretty much anything that roles, pre_tasks and post_tasks can do as well, right?
Thank you so much for your help, that clarifies things for me 
Stay safe!