Hi.
This actually depends on the needs of the client.
If they want to do detailed scheduling easily, and have s-curve etc.. it is actually easier and faster to to do it in MSP. The MSP also has the advantage that no need for SAP user license for all persons making changes to the MSP (but you need a SAP user to connect the MSP to SAP).
The disadvantage of MSP is that there are more uncontrolled source of data. The data updates are not real time since you still need to trigger the update of the projects. The MSP data is not integrated witht the rest of the SAP modules unlike if you perform the functions direct in SAP standard.