We have a large number of existing project sites in SharePoint and now would like to manage those projects in Project Online. We see that we can add the SharePoint project site to PWA and then Activate it to manage the tasks via PWA. We are trying to decide whether to continue in this mode or to create future projects in PWA and use the PWA project site for future projects. Would like some input on which approach would be most beneficial from a Portfolio and Resource (Engagement) Management perpective across projects, or whether the location of the project site really matters: 1) All project sites within PWA 2) All project sites wihthin SharePoint Online 3) Hybrid - SharePoint for older projects, PWA sites for new projects going forward.
From a portfolio view, of course, I would recommend to include all active projects that have active resource engagements in Project Online to have a complete overview. So you can already exclude projects that are inactive or already closed.
Now comes the technical part:
In Project Online, from a support perspective, all project sites need to reside in the same site collection as the PWA instance. So you might have to move your "SharePoint-based sites" first to a single site collection, if they are dispersed and you want to integrate them.
To manage your portfolio and resource engagements, a project site is not required. But it helps if you want to aggregate risks, issues and other SharePoint data for your portfolio reports. On top, you provide your users a single entry point to find their project documentation