@paulminors there is another case in which I heavily use additional projects and I completely forgot to mention: automation!
I use Zapier for a lot of things, and because I use asana as CRM as well, I am not using my mailbox to see which emails I need to reply to, but I converge all the emails as tasks in asana.
As Zapier does not have the possibility to search subtasks, I have some projects (which I don’t use directly) which only reason to exist is to give Zapier the ability to find subtasks.
Every time I receive and email, I add the content of the email to a subtask of my contact. (and I do this to have a centralised repository for contact information without using a CRM *). In order to do so, my contacts have a subtasks with their email address. This subtask is part of a project called “Timeline”. When I receive an email, Zapier looks for the sender email address in Timeline, and when it finds it I can link the contact to the email.
* for how much nonsensical it may seem, for this specific business I don’t want to have an additional CRM that duplicates information I already have in Asana. Hence I bypass the need of a proper CRM using asana for it. If only mailtrack.io would offer a public API to identify when an email has been read, I would rule the world by creating automations just between gmail, asana, zapier and mailtrack