I'm not sure I am experienced enough to give you an answer that us correct but I can tell you a way that I used it yesterday
I received a request as part of a larger project I have been working on o procure software from 8 different licensors. In order to do that I will need to meet with and collect information from 5 technology people. Then I will need to meet with and collect information from 3 vendor managers. Finally I'll need to contact the licensors.
I set up 8 projects, one for each vendor. The meetings with the tech people may only take about 1/2 hour but there are several discrete actions that are tied to the meeting with each. So the main action is to have the meeting. That will involve identifying the correct person, setting an appointment, meeting, I have a checklist of the information I need. Since these projects are generally the same in actions needed, but have different combinations of tech people and vendor managers, and I would guess different response times for getting me the information I need, I have to be able to track where things are in the process but be able to see at a glance that the larger, meeting tasks have been completed
Additionally, half of the licensors are new, so I'll have to run through a series of actions that apply only for the initial acquisition from a vendor. I pull this series of tasks as a main tasknwith subtasks into every project as it is easier to swipe, delete the main task and all of the subtasks when they aren't needed than to copy and paste them in only when needed.
These aren't sufficiently large or complex to really require them to be separate projects