Причин много. Вот например выдержка из Analysis Services Operation Guide :

The meta data for the objects created in an Analysis Services instance (the cubes, dimensions, and so on) are stored in the Analysis Services repository. By default, this repository is a Microsoft Access database named msmdrep.mdb and is stored in the ..\Microsoft Analysis Services\Bin folder on the Analysis Services computer. The Access format is used so that users who do not use SQL Server for relational data can still use Analysis Services. However, if you do use SQL Server, migrating the repository to a SQL Server database adds enterprise-level scalability, support, and security. Migrating the repository also enables you to perform coordinated backups of the repository database with a file-based backup of the Data folder. For more information, see "Backup and Recovery" later in this paper.

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