Here is some information from Microsoft's web site on the benefits of splitting your database:

Benefits of a split database

The benefits of a split database include the following:

* Improved performance The performance of the database usually improves significantly because only the data is sent across the network. In a shared database that is not split, the database objects themselves — tables, queries, forms, reports, macros and modules — are sent across the network, not just the data.

* Greater availability Because only the data is sent across the network, database transactions such as record edits are completed more quickly, which leaves the data more available to edit.

* Enhanced security If you store the back-end database on a computer that uses the NTFS file system, you can use NTFS security features to help protect your data. Because users access the back-end database by using linked tables, it is less likely that intruders can obtain unauthorized access to the data by stealing the front-end database or by posing as an authorized user. By default, Windows XP, Windows Vista, and Windows Server 2003 use the NTFS file system. If you are not sure what file system your file server uses, ask the system administrator. If you have administrator privileges on the file server, you can run the msinfo32 command to determine the file system yourself.

How do I use msinfo32 to check the file system?
1. Click the Start button, and then click Run.
2. In the Run dialog box, type msinfo32 and then click OK.
3. Under System Summary, click the plus symbol next to Components.
4. Under Components, click the plus symbol next to Storage, and then click Drives. The dialog box displays information about the available drives in the panel on the right.

* Improved reliability If a user encounters a problem and the database closes unexpectedly, any database file corruption is usually limited to the copy of the front-end database that the user had open. Because the user only accesses data in the back-end database by using linked tables, the back-end database file is much less likely to become corrupted.

* Flexible development environment Because each user works with a local copy of the front-end database, each user can independently develop queries, forms, reports, and other database objects without affecting other users. Similarly, you can develop and distribute a new version of the front-end database without disrupting access to the data that is stored in the back-end database.