When using security on dimension content in SSAS, one point of confusion is when a person sees the grand total for a measure that includes the total of ALL members for the dimension in the cube, even though the security has limited the members that person can see. To fix this, check the “Enable Visual Totals” check box, so that users can only see the total for members they are allowed to see. It is located on the Advanced tab on the Dimension Data tab, near the bottom.
For example, let’s say the total revenue for all the divisions in a cube is $15,000. You create a role called “Division A”, and set it up so members of that role can only see the revenue for Division A, which totals $3,000. If you use a front-end tool like Excel to access the cube and use the division hierarchy to see the total revenue, you will see the revenue of $3000 for Division A, but will also see the Grand Total for the revenue as $15,000. This is because the “Enable Visual Totals” box is not selected (which is the default). Selecting this box would result in the Grand Total showing as $3,000.
Reference James Serra blog