By default after 180 days or some number of mounts, most Linux filesystems force a file system check (fsck). Of course this can be turned off using, for example, tune2fs -c 0 -i 0 on ext2 or ext3.
On small filesystems, this check is merely an inconvenience. However, given larger filesystems, this check can take hours upon hours to complete. When your users depend on this filesystem for their productivity, say it is serving their home directories via NFS, would you disable the scheduled file system check?
I ask this question because it is currently 2:15am and I'm awaiting a very long fsck to complete (ext3)!