Tape backups of the server are taken every day or weekly depending on your hosting package. These are taken in the event of a worst case scenario eg servers' hard drives breaking and the entire server needing restoring.
We are unable to restore individual files or web sites. Backups are taken purely to restore entire servers in the event of hard disk failures or something similar.
We would recommend making backups as a matter of routine so that in the event of data loss it wont pose an issue, but if you do lose all data it may be retrievable for an additional fee.