How does the workflow setting work in 'Types de projets' ?

Hello all,
We have already Workflow settings in severals settings like 'Types d'activitées', 'Types de documents'...etc and all of these settings are hierarchically attached to the Project.

I understand that we can choose different workflows on certain parts of the project but what is the function of this settings placed at level project ?
On which part of the project does this setting have an effect excately ?

Thanks you.