What are different options or variations in Timesheet in Project Server 2019

Hi,

For Timesheet In Project Server 2019 on prem, 

For Project Level Reporting or Top Level Reporting
I have 2 questions :

1 - Unless I assign the resource against task, he is not getting timesheet generated for him
For Top Level reporting- I thought  resource assignment is not needed against task

2.1- What is the benefit of this piece of functionality ? any scenarios if someone can share ?

2.2 - Where can I see the summary of report generated by this approcah...

Appreciate any  suggestions...