If a database has two or more tables and an update process involves changing more than one table at the same time a physical snapshot of the file onto tape could catch the data in an inconsistent state. If this happens and you restore the backup you may get a database that is not usable. For example, a table might have in it a different number of records to the table header so that Access becomes confused. In effect you do not have a real backup.
High volume production databases such as MS SQL server or ORACLE have the database itself do the backup by copying the tables from within. They can do this because every change to a table is logged so you can rebuild a table from the last good copy plus the log.
Ken
Backup of an Access database supporting a web server is particularly important as there have been cases of file corruption when input is through a web front end.
If possible, I would suggest you set up another database - link through to the tables on the server database and use the link to import records added or changed since the previous backup.