Hi,
Don't get ferocious Fery.In PP you can do all such things what we are doing in PS.But If you have more and complex activities , you need PS for scheduling,budgeting and to plan cost/revenue and collect costs/revenue .Based on milestones you can invoice the customer or make payment to vendors.Based on progress analysis you can findout the status of your project at any point of time so that you get good control over the project.You can integrate Investment management module for Capital investment project.Finally you can settle to COPA or cost center or asset.
PS will do more lots of things since it is integrated with almost all modules.
If you still need more information about the process contact me offline .
[email protected]
Anbudan,
FATMAN