Baseline a project, update a project question

Hi,

I have been planning now for just under a year now and starting to find my feet...

I have a question about when to baseline and re-baseline projects

So i have been collecting all dates, resource, cost ect and building my plan, i have got the client/customer/designer etc to agree the plan and from there i set my first baseline.

When changes are made, for example

1. New work that is out of the project scope is added as it was missed from the original tender

2. New resource is added or swapped on an activity

Do i re-baseline for both of these?

I am using Primavera P6 and it gives you the option to add revisions on your set baseline, do i use a new revision or set a new baseline when re-baselining?

hope thats clear enough!

Thanks

John