Following on from my posting a couple of months ago (2/1/2016) when I highlighted this coming change for our Project Online customers https://blogs.technet.microsoft.com/projectsupport/2016/02/01/project-online-resource-engagements-news/ you will see starting this week that all new PWA instances, either new tenants/customers or just new instances in an existing tenant, will have the resource engagement feature turned on by default. This means that you will not have the old resource plan capability in these new tenants. This will have been on your message center for he last couple of months so shouldn’t be a surprise for existing tenants – but if you are new to Project Online and perhaps have come from Project Server 2013 then this will be new to you. I suggest starting with the product group blog post as a good intro to Resource Engagements - https://blogs.office.com/2015/06/19/resource-engagements-coming-soon-to-project-2016/. Another great recent write-up appeared on the MPUG blog from Jeremy Cottino - http://www.mpug.com/articles/understanding-resource-engagements-in-microsoft-project-2016/ (You can ignore the initial piece about activation – as you don’t now have the choice – it is turned on by default). Or if video is your thing, Spiro Theopoulos has this walk-through for you - https://www.youtube.com/watch?v=iYP2coO4AjI. And the FAQ for Resource Engagements can be found at https://support.office.com/en-us/article/FAQ-Resource-engagements-are-replacing-the-old-resource-plans-5ddd3242-4858-4e57-a8c1-2b20c06d959a.
One thing I’ll add from the support perspective for resource engagements and capacity calculations - as this setting has been tricky to find for some users – when using resource engagements and wanting the resource utilization to be calculated based on the resource engagements for that project, the setting is in the Project Information dialog for the plan from within Project Professional 2016 (or Project Pro for Office 365). If you were used to Resource Plans before then this was on the web page. The same options are available – so you can calculate from the project plan to a certain date – or just from the Resource Engagements.