Siebel Forecasting Guide > Matrixed Sales Organization >
About Adding Overlay Managers to the Sales Team (End User)
This option guarantees that overlay sales managers can see their subordinates' opportunities, but it means that a large number of people will end up on the sales team, a large number of opportunities will be synchronized, and you will have to do a lot of territory administration work when reporting relationships change.
Mobile sales organizations might want to consider the impact on synchronization times. You might end up providing the overlay sales managers with more information than they really want on a mobile client.