Vinod:
The Timesheet Cube shows actual work reported through the timesheet. The
MSP_Project_Timesheet shows actual work recorded in the Project file. There
are numerous reasons why these would not be in sync, including bugs in the
Project client that have just recently been resolved in the December 2009
CU. With that said, bugs are the least common reason for discrepancies
unless you're using the Project Server setting to restrict updates to actual
work from Project Web Access only, which locks down the system rather
tightly and not a practical option for many organizations.
So for example: Suppose a PM updates a task status directly in the project
plan where a resource is assigned. This imputes actual work that will never
show in the timesheet cube. As this is a very common practice, in many, if
not most cases, you are very likely to see more actual work registered in
the project plan than in the timesheets, unless of course, your PMs are also
in the habit of deleting completed tasks, which would have the exact
opposite impact.